Concerning the first question, It allows you to connect external scsi devices such as external scsi iomega (zip and jazz) drives, external cd-writers and possibly external harddrives (this point needs to be researched). Clearly, one might not need it as much since it already comes with internal cd writer. Now, if one can connect directly to external scsi harddrives and if one can record songs from Genesys to the external harddrive directly, this will solve the limitation of 2GB of the harddrive.
2GB is enough to store midi songs, styles, and sounds.
But it is not enough to store complete audio songs. In my humble opinion, one needs at least 20gigs. But the point of GEM is that one can write these into the cd-writer and they have good point.
When one wants to use the audio recorder on the genesys, it is not to do professional recording but quick audio recording which can be transferred later to audio recording station or eventually be burned on a cd. Therefore, the limitation is not that big of a deal. For me it will work wonders and will save me lot of effort.
I, for one, record professionally but also find myself recording quick demos to be performed at churches. Genesys would save me a lot of work.
My only objection about Genesys is its weight. But hey, my sk880 is heavier but it works great in the studio. And sk880 has 88 weighted action. Genesys 88 maybe the replacement of sk880.