I used to use sound modules, I had a roland dedicated bass and drum module, don't remember the name. I also had a E-mu Proteus 2000 great sounding module six outputs, and a Peavey bass module also nice sounding. I've also had a couple of the Roland sc 55 GM modules, also very nice.
Then I got a Tyros it has enough outputs, great sounds, hard drive, connectivity. So I sold all the modules just got rid of the last one last month on ebay.
I ususally use power tracks pro computer based sequencer. Don't even know how to run the sequencer on the keyboard. I think one of the advantages of a computer based sequencer besides, mouse, larger screen, storage, compatability, when I get a new keyboard I don't have to learn a new sequencer.