I had the Pioneer's hooked up to the B channel of my Denon for a couple of days prior to my last audition.
Without the purchase of an AB selector it was a little difficult to transparently switch back/forth as the levels were off due to the ohm difference.
Anyway, I was very impressed with my old Pioneers. Personally, I thought the detail was right up there with the m80's. Also, they may have had a bit more in the bass category compared to the 80's with no sub on, due to the 15" turbo woofers. Throwing the sub in the equation it was a toss up. I had more overall bass presence with the 605's because of the additional air movement of the 2 extra 12" woofers added to my 3 subs.
I also played around a little with small/large settings on the receiver to pump out more bass to the loudspeakers and they handled it well with no strain.
Honestly, I was very impressed with the sound I was hearing, maybe I should sell my 80's. Just kidding.
I can say I won't be selling my old Pioneers anytime soon, just what to do with them?
I do have an old JVC pro logic receiver I could use it for 2 channel music listening with my 605's..