If you aren't able to certain Roms working on either client, you must make sure to use Rom Versions matching the version of MAME running.
Not Recognized? Make Sure Your X-Arcade™ Is In Mode 1
Most problems are accounted for by checking your in the right mode. While someone like Woz would love it, it's quite an annoyance to us Mac™ users just trying to relive some classic arcade games. Mode 1 is the default mode and if you're switch is moved closest to the serial port, it's fine.
If it wasn't in this spot, move it there, then push the button on the back of the X-Arcade™ twice (the light on the X-Arcade™ should turn off from the first push, and back on with the second) and you will load Mode 1
The MAME™ software includes a "Help" menu that can help you (press F1 on your keyboard to access). Alternatively, here are some more very helpful sites that have more in-depth MAME™ instructions, troubleshooting help, and information: