So.. you could use the floppy drive and cassette or whatever peripherals, but wouldn't be able to use any of the A8 software. Would be cool for some homebrew stuff.
I haven't ever used a 7800 wasn't it (hardware wise) somewhere between the Sega Master System and NES (better than the NES, but maybe not quite as powerful as the SMS?)
Atari 8Bits: 800xl, 600xl, XEGS, 800, 130xe, 130xe (VBXE, U1MB, Stereo POKEY)
Atari STs: 1040STf (broken shifter), 1040STe, Mega STe, TT030, Falcon (CT60e, SuperVidel)