Sam, I think the VTF-2 MK4 would be better for your size room, and it does have much better low bass output. I'm sure either one can mate with your 601's.
No, I have not heard the HB-1 MK2, but suggested them because of the excellent reviews.
After looking back at the years when the 659 was current, it was probably the 601 S3 we sold at that time, although I do have experience with all of the 601's. As I said, the most difference is between the original and the S2. Again, for a perfect match get S2's to match yours, however, S3's would probably work fine, but definitely stay away from the original.