apart from selecting, starting & stopping the style from VA, all the rest could be controlled from the Audya. Every Audya button can control vArranger, but be carreful because this will also select things on the Audya. So for example, if you press VARIATION B button, it will ask to vArranger to change variation B,but will also do it on the Audya. It's not a problem, but imagine for example the DISK button of the audya it can control vArranger, but will also go in the disk page of Audya. So not every button can be used

Can the Audya be the only source for the sounds without using a PC sound card? YES

Thus, I would need ONLY the USB cable between the PC & Audya. YES