Picked up a 6500/275 since I wanted a tower system and there was one for a non-confiscatory price. It works fine in Mac OS 8.6, including audio. It has the AV inputs, but no AV out (other than the usual audio jacks).
In BeOS R5, it mostly works great. The Twin Turbo card works, the DEC 21140 NIC works, it’s nice and zippy with a 1MB L2 cache card, but … the audio doesn’t work. I even tried turning SRS surround off in MacOS to see if that was affecting anything, plugging in headphones, external speakers, nothing. It’s silent as a post in BeOS.
Anyone have a 5500, 6500 or TAM running BeOS? Does audio work for you?