On the old PA1x they had a setting "BEST GM SOUND", and what this did was to select an appropriate sound from the soundset to play the GM file gave a good result, but not as good as editing the file and replacing with higer bank sounds/insert effects.
For some reason they have dropped this from the current PA series, but I think instead they have done what Yamaha have done on the Motif series, in that they have really tweaked the GM soundbank to be as good as it can, even to the point of adding additional samples.
If you load in a SMF that has been sequenced properly, it will sound fine on you PA800, and there is not much you can do, (without editing the file itself) apart from modifying system effects.