The G91 will play DVD-A discs whilst the G92 will not. I think that's the main difference...I'm not aware of any others, but I haven't looked closely at the spec sheets.

There were different versions of the G91, the G91DH (aimed at DSP users), G91AH (aimed at analogue users)and G91A (handled both), and G91A DAB (handled both, and had FM/DAB instead of FM/AM). I think the G92 directly replaced the G91A and can also be had with or without DAB.

Cheers

George