afaik audio passthrough has been working on all builds for a while now.
as for choice of board the Raspberry Pi4 is likely to have the best overall community support and quality.
but imho the Orange Pi 3 LTS is much cheaper and will provide the same performance as any of those boards. but then again I'm biased because i have several OP3s, and the more other people I can convince to buy them the more likely it will receive long term libreelec support 
Raspberry Pi 4 has the best support, but its hard to find/or expensive. I have had great success with Orange Pi 3 LTS, its cheap and available, has built in eMMC and plays everything just as well (imho) as the rpi4. Only thing with the OPI3 is that it won't have wifi support on LE. Either way you would want to get heatsinks/fan for either one. That giant heatsink that comes with the N2 is a nice feature.
how does that behave if you use the same remote you use for your tv ?
depends how lucky you are. It worked well with very simple TVs that had very complicated remotes. Often a TV remote will have play/pause/stop buttons that would only work if you happened to buy a vcr or DVD player of the same brand. Those buttons can safely be mapped for this kind of use. I think on my old Toshiba (long dead) there was a button or function to put the remote in DVD mode. The volume buttons would still control the TV, but play/pause stop and even the arrows and menu buttons would not do anything to the TV in that mode, so i mapped their codes to be by my psuedo-flirc. I just had to keep reminding family members to put the remote in DVD mode to use the raspberry/Kodi.
Do these devices work straight out of the box?
lol, no, you shouldnt try this unless you are in the mood for a science project and you like tinkering. If you need something that works out of the box spend a few extra bucks and order the dongle from FLIRC.
But to answer your question, the VS1838 IR receiver itself does not need to be configured, you just solder it onto the arduino board. It has pins for gnd, +5 and signal. use any available digital input on the arduino for the signal pin. Some wiring examples show adding a pull-up resistor, but mine worked without it.
But you need to download a program to the arduino. I attached the program I used, but unlike the nice setup-mode of the FLIRC, here you would need to play around and figure out the codes for your specific remote. The codes in this program worked for the Toshiba and samsung remotes i had at the time.
The program itself is actually very simple, all the heavy lifting was already done by the IR-remote and keyboard-emulation libraries provided by Arduino.
I built several of these years ago for all the non-CEC capable TVs in the house. I never heard of FLIRC until recently, but these basically did the same thing. The arduino emulates a USB keyboard and sends appropriate keystrokes based on the IR signals it receives from the TV's remote.
in the pre-covid days I was buying bunches of these generic pro-micro arduinos for less than $4 each, and the VS1838 IR receivers for 5 for $5. sadly, the chip shortage has pushed up the prices of arduinos...
am on the waiting list for a RPI 4
Why not order an OrangePi 3LTS? its available, its cheap, it plays everything the RPI4 can just as well (in my experience). And it has Emmc so you don't have to worry about an SD card wearing out. no wifi though...
Using the latest Nightly from Feb 13 for the Opi3Lts, I now have CEC working!
Thank you to the developers for their hard work!
I also admit that part of the problem might have been on my end. Even with the new image CEC wasn't working, at first. My LG tv has a stupid feature called "magic remote" that is supposed to remember and auto-recognize certain devices (this is why my TV was showing the Opi as "FLIRC", it was not something being reported by LE).
ANyway, I managed to delete the magic-remote settings, power cycled my TV, and now all is well.
after about 10 times power cycling, it happened again. No LEDs on the ethernet port and no network accessible from LE.
I was having the same problem (documented here) but its intermittent, so if you try power cycling a few times it should eventually work. (at least the hardwired should work, not wifi).
Here's some more info that might help. I attached the results of the "cec-client" command from both the OrangePi and from a working Raspberry.
Everything starts out pretty much the same, they are both successfully doing CEC writes and reads and getting the same replies from the TV. But then about halfway down the Opi starts getting "Write - ioctl CEC_TRANSMIT" failures with errno 22.
The pulse-eight github page does not list Allwinner or OrangePi as one of their compatible devices. That would seem to explain why I can't get CEC working on my Opi3LTS (LE tries to use the Pulse Eight driver).
But I see from this post that at least once before someone got LE and CEC and Allwinner working together.
So did older versions of LE use some driver other than pulse-eight to interface with CEC on Allwinner? Or is the Pulse-eight website being overly modest by not mentioning Allwinner compatibility?
Can you please test this update?
The board no longer reboots when the pulse-eight adapter initializes, but TV remote doesnt actually control it. this is the same TV and cable that works fine with Libreelec on a RPI4.
heres the log:http://ix.io/4mb5
can be flashed on an internal chip (NAND),
log in via SSH and run install2emmc
log files:
intermittently, the ethernet port will fail to work after a reboot. Other times, it will eventually work but the boot process will be significantly longer and there will be a longer than usual delay before the LED on the ethernet port starts blinking.
If I check dmesg after one of these long boots I see the "NETDEV WATCHDOG: eth0..." fault. (it also shows up in the attached log). It dumps some diagnostics into the log, resets the ethernet adapter and then after a couple seconds i see the "Link is Up..." message.
the occasional delay i don't mind, but when it never resets and the port stays dead is a bigger problem. 
I think I collected the logs correctly:
Things were happening a little differently now though. After kodi boots, once i see the "Pulse-Eight CEC.." message in the top right the OPi freezes and automatically reboots. It would continue in a boot loop, unless i unplugged the hdmi and plugged it in with a cheapo hdmi cable (that doesnt have the CEC channel). hope this helps.
I have an OrangePi 3 LTS running the newest v11 nightly (ethernet port won't work with v10 images).
My TV remote can control my RPI4 through the HDMI CEC with no problem. But with the OP3, the TV recognizes it as "FLIRC" in its CEC setup, but doesn't actually control it.
Is there some trick i need to do in the OP3 to make it emulate a FLIRC? Or is there a limitation in the hardware CEC implementation of the H6? Or is this just a limitation/bug in the nightly images?
Thanks! I also found more info on Sandmann's github page and I get the impression from reading the comments there that the problem is "fixable".
I followed Chewitt's instructions from a few weeks ago to setup Amazon Prime video using the Sandmann repository.
It didn't work, but then I saw CvH's post from Jan 2nd that Amazon VOD won't work after the new year.
Is that a temporary glitch? Or has Amazon done something to permanently put the kibosh on Prime access through Kodi?
