There's no difference between panel and XG voices when it comes to effects - there may be a difference in the software you use, however. For example, none of the XG editors I've used have panel voices because they've all been designed for XG synths. I've had to update XGworks, XGEdit and XGGold to get the panel voices. And none of them address all the effects and their parameters without further updates. I only use XGworks now because it's the only one that can address my whole synth. If you use the XGworks XG editor on your 2000 you can layer several voices and apply all 5 DSPs in any combination to one or more voices. That way you can 'improve' the XG voices or mix them with the panel voices.

Generally speaking, the XG voices are the same across all keyboards. This is for compatibility. It's the panel voices that get the improvements, often layering two or more sounds as well as increasing the size of the samples. I was comparing a 9000 and 740 side by side the other day, and I was using the styles and XG voices. For example, playing a number with the Atmosphere pad and the Big Band Ballad I could detect no difference between the keyboards. Neither could anyone else.

Bryan