AFAIK, the A/V daughterboard on the 8500 had video input and output connectors, while the 7500 had input only.
Love that 7500. My first Mac, actually. Dad still uses it for music score editing (and playback!)
2xSE/30, Colour Classic, Mac II, IIx, 3xIIsi, LC, LC475, LC575, Power Quadra 700, Quadra 840AV, 2x5200, 7200/90, 7500/132, 7500/233, 7600 G3/450, PowerBook G3 Bronze, iMac DV SE, MacMini G4, MacMini Core2Duo, iMac 21.5" i5... and SGI Indy R5K