(TL;DR version below )
I've been looking up some info for a music ('dj') pc I'd like to build and have some questions. Not all of them are related to HATs but it seemed a good idea to ask everything in one post as to explain what I would like to achieve. If this is against forum policy, my apologies, I will ask some questions in other sections of the forum then.
The setup I'm interested in is as follows: a Pi4 with a DAC HAT (PiFi, HiFiBerry, ...) running Raspbian Buster with Mixxx, a browser (for youtube mainly) and possibly Spotify.
There are no external controllers or anything, Mixxx is mainly used with the auto dj function, with automatic crossfade (Mixxx also offers manual fade, a feature other software seems to lack, which is the reason I chose it, although most of its other capabilities will not be used).
Mixxx would only use one analog output, connected to one channel on the little hw mixer I have, as well as a headphone output, both on the DAC (i.e., I want a DAC with 1x analog 'master' output and 1x amplified headphone output, e.g. the one in this PiFi package, or this one from JustBoom.)
All other applications should use the on-board output, connected to the second channel of the mixer. It doesn't matter if the sound quality of that output is a bit inferior. However, if sound quality/performance issues are to be expected and there's fixes for that, I would be interested.
The music collection is pretty big but should fit together with the OS, which is small anyway, on a 256 GB SD card (which I would partition, possibly using LVM, I'll see), including some headspace. This would keep the entire system nice and small, with no need for a usb drive. I suppose there's no reason to think this is a bad approach?
I'd prefer a Pi4; I know that HiFiBerry confirmed their DACs work on the Pi4, I don't know about for example a PiFi... Can anyone confirm?
I'm an experienced Debian user but have never used Raspbian, although the differences should be small I guess. I have no idea if pulseaudio gets installed by default on Raspbian Buster, but I know Mixxx doesn't like it and suspends PA by default. Although this behaviour can be changed, I hope I can get it running properly without PA, for example by simply having the on board sound card as default output (in ALSA). Then I won't have to deal with the latency that PA introduces. Can anyone comment on this? Is there a difference between Debian and Raspbian, setup-wise? I guess I have to make sure both sound cards are enabled in /boot/config.txt?
So, for the TL;DR version:
*Does anyone know if DAC HATs confirmed to work an a Pi 3, like the ones I mentioned from JustBoom and PiFi, work/fit on a Pi4? HiFiBerry confirmed theirs do, but they don't have a model that suits my needs.
*Can I use the on-board audio outputs together with the DAC outputs? What is needed in /boot/config.txt, and what is the easiest way to have the on-board card as the default one, so applications use it unless configured otherwise? I don't want pulseaudio, also I don't need software based mixing between the two cards as I have a hw mixer. I can set the DAC as master and headpone output in the Mixxx settings.
*Storing the OS and all the music in partitions of a 256 GB micro SD card keeps the system nice and small, and provides the possibility of having a 'hot spare'/backup. Are there any reasons why this would be a bad approach?
*Are there any relevant remedies for the sound quality issues of the on-board sound card, if any with the Pi4?
Thanks in advance for any answer!