Regarding memcards, at least for AES I tested Unibios 3.2 support for 16bit PCMCIA SRAM cards.
I happened to buy a Pretec 128KB SRAM and noticed that the NeoGeo official games [well one of them at least] had no trouble with it but Unibios 3.1 didn't quite like it.
A quick back and forth with Razoola and 3 BIOS patches later to UniBios 3.1 and it worked like a charm (with support for splash screen bypass and hiscore as well). Razoola discovered that SNK embedded support for 16bits PCMCIA SRAM cards in the original bios way back when so he found a way to "fix" Unibios to work as well.
I am not saying that all 16bit SRAM PCMCIA cards will work but it may be worth a try ... 128KB worked for me (and I have yet to reach the mem card full , and I saved HS and in game for quite some games, say 30 or 40 "unique" out of the 161-in-1). Maybe 256/512 or 1MB work as well, who knows, but make sure they are not Flash but simple SRAM cards if you want to try.
At the time the Pretec 128K was very cheap, around 30US$, now they seem much more expensive and bigger in size (not sure they work or they are worth the extra money) but on eBay I can see quite a few "reasonably priced" 256KB and 512KB ... (btw most of them do take a CR2032 as a backup battery, without the SRAM loses it's content in a few days of non usage in my experience).
Anyway just thought of putting it out here so if anyone wants to give it a try you have one case that worked, me (and it worked because Razoola made me test UniBios 3.2 until we made it to work, but he said he was in touch with some other guys to get more coverage for 16bit PCMCIA SRAM cards support).