TTx3 multi will give you 2 player in a lot of games. Basically if a game supports 2 players locally then it will work for 2 players for that game. Just a bunch of games are either single player, or they can only be played as 2 player across the nesica live network, which is effectively a proprietary networked cabinet setup. These games are built so if you want to VS play against another player it has to go through the nesica network, which taito owns and runs, and you don't get access as you aren't an arcade operator and you aren't paying taito... Some other systems which require network play for VS can be linked, like the Tekken series, but anything Taito/Nesica, if it doesn't support local 2 player then you are stuck single player for now.
Sf5 is a TTX4 game, it just happens to run on the TTX3 hardware as well. Single player local only. If you want 2 player, the pc version will give you that, you just run it on a pc in your cab using brooks board or something like that for controls.
Google artax multi for TTX3, has a fair few games on there TTX1/2/3, etc etc. It has all 3 SF games on there. I know 3 3rd is 2 player, not sure about ultra sf4 and i know sf5 arcade is not local 2 player. If you need 2 player local for sf5, then pc version. It's better pc version anyways, the arcade dump is still basically the first version of the game, so it's really old. The only sucky thing about hte pc version is requiring more buttons than you generally have available on your cab to navigate all the menus (enter, esc, etc), so you need a keyboard or more buttons in your cab to navigate the menus.
