I wanted to add some recent experience I had. I just want to put this here in case anyone comes along later with similar troubleshooting issues. None of this is complaining, love Raz's work on the Unibios.
My hardware:
I have my Unibios 2.0 (which I am 99% sure I got from Raz around release). This was installed in the MV-4 board in my Big Red in 2004ish and was still in there when I bought it back.
I got a Unibios 4.0 with a soft reset patch to work with a Vortex All-in-One cart (modded 161-in-1) I got both the cart and bios from leonk.
I ended up with an MV-1A that had a Unibios 3.0 already in it from buyICnow.com. I bought this board mostly to get the unmodded 161-in-1 V3 multicart that came with it.
My issues:
The 2.0 bios seemed to work just like I remembered with the four carts it came with (SamSho1, KOF98, Slug X, and Windjammers). But I also did not use it extensively before getting the All-in-One and putting the patched 4.0 bios in.
With the All-in-One, the patched 4.0 bios worked as expected, I could soft reboot back to the menu. I mostly used this cart until I acquired a few more real carts. Once I did, I loaded up the four slots and started to notice some sound issues.
I found the comments from earlier in the thread that it is a known issue for multislots with 4.0 to need a cart in Slot 1 otherwise won't have sound. But beyond that, even with a full board, letting it cycle I would lose sound when it returned to the splash screen in attract mode between Slot 4 and 1. Sometimes on the first time through, sometimes it would work for a while but it seemed like no matter what I did, if I left it running in attract mode, eventually sound would drop out and the only way to get it back seemed to be a power cycling the cab.
Also as a minor issue a Ghostlop cart (I don't know the donor cart it's a PROG 4096 and a CHA-256, and chips are again from buyICnow.com) would show a garbled name in the Soft DIP settings as seen below. (Showed this way whether it was the only cart or if there was a full board).
My fix:
Ultimately I decided to try putting the 3.0 bios in my 4 slot, so far I have run three hours each on attract with two different combinations of four carts (four originals in one group, then three different originals and the Ghostlop in the other group) and still have sound.
The Ghostlop display name issue in the Soft DIP menu is also fixed. (this was taken before I reseated KOF98 in slot 2)
I suspect the 2.0 bios would be stable as well, but I'm not going to disassemble the board again at least at the moment. I put the patched 4.0 in the MV-1A and will likely just swap the board entirely if I want to use the All-in-One or PickNmix with the unmodded 161 and just use original carts with 3.0 on the 4 slot.
& 
github.com
