Well so far I've been listening to the Optonica SA-5201 in the main system replacing the Sansui 331. The Optonica is nice. I like it very much. If the Sansui is described as 'warm' in it's overall sound then I would have to say that the Optonica is very 'clean' - not as thick in the bottom end as the 331, but in no way is it 'bright'. To be honest when comparing it to the Sansui the Optonica occurs as much less 'coloured' (I do realize intellectually that it is more likely just a different kind of colouring), the overall sound seems more natural and even-handed.
The tuner on the Sansui seems to be more sensitive, as in my basement, with no antenna, it can still pickup local the station in clear stereo where as the SA-5201 will only pick it up with that classic 'HISSSSS' until I hook the antenna up to it.
Haven't tried the Optonica in the secondary (living room) system ( the one with the Optonica RP 7205 turntable) and not sure I'll bother as the Marantz works well there and my wife likes the looks of it, plus I really like the sound of the Dynaco A-25X's with the extra power of the SA-5201.
Now the question is what am I gonna do with that Sansui 331? I still really like it and don't wanna get rid of it. Tomorrow I am going to look at a AR-XA with a Shure M91ED that's supposed to be in fine running order and has a very reasonable price attached to it, so maybe I'll pair the 331 with the AR-XA in a bedroom system. If I do I'm gonna need some speakers. . . HMMMMMMM, I wonder what would work well with those two units?