Let me get your post straight.

You liked PSR2100. However, you sold it because you did not utilize all the functions and you bought PSR550 for probably half of the price. You found that its sounds are adequate but the speaker is not. So you are looking for a keyboard, it does not have to be an arranger, with decent quality of sounds at least like PSR550 with good speakers and the same price as PSR550. Or you want a synth with the same price range that will work with the couple 12inch amps.

It seems to me that PSR2100 was a perfect fit. Also have you considered the following:

Yamaha DGX500 or DGX300?