I think it is an understatement to say that the VA-7 is a sampling workstation. The PSR-8000 and 9000 are sampling workstations. However, sample loops on these machines are not readily synced to autoaccompaniment. The strength of the VA-7 is that audio loops can essentially become part of the style. My understanding is that the Solton X1 incorporates live loops into its styles, and that these add much to the appeal of the X1. However, the X1 is limited to unpitched instruments and the loops are fixed. The VA-7 allows pitched instruments and you can add your own. If you can get ahold of the Roland Demo Tape, this will be clearer. Sorry, I do not know about voice editing on the VA-7.
I might add that I do not think people are going to discard their X1s and PSR-9000s over the VA-7. However, the VA-7 does add an excited new dimension to autoaccompaniment.