I'm a play by ear bassist that would like to add some background synth sound and play bass lines with the same instrument. I looked at a Yamaha SO8 in Pittsburgh early last summer and a Roland RS 9. Also I'm curious about a Yamaha PSRGX76. My search has been focused on 76 or 88 note boards. I'm a beginner in all respects but would like a good quality instrument. What's your opinion? Thanks for your help.

Yamaha just introduced new keyboards to replace the PSRGX76 . The new models offer a disk drive which I think is important for practice .
Play midi sequences and eliminate the bass part !

And have decent sounds and styles to work with . dano

Is a synthe really what you need? Seeems to me that if you are wishing to do this primarily to practice your instrument, what you need is to get some long loop sound files to play along with, having synthe backrounds or whatever you wish. I would not suggest buying a keyboard for this purpose only. If you wish to learn how to correctly play a keyboard, there are ones that are designed specifically for that purpose.