One difference is the tone arm. The new 9.1 has the single piece carbon tonearm, the 9 has an head shell which is stuck on. I have not heard either, but the reviews make it out that the difference is a big one. If you plan to push up the cart to high levels, the tonearm would become a constraint. For most mortals however the rpm 9 tonearm should be fine.
The new 6.1 has the same tonearm as the old 9 (but not the old 6.1). I suspect the 6.1 table would not be anywhere as good as the 9. the basic drive mechanismare are different. The 6.1 is basically a souped up entry level turntable, the 9 is serious stuff. Perhaps you could change the tone arm at a later stage if the bug really gets to you.