Slip-on, I have the m-60s with the rxv-1500, there are many opinions on the type of sound each receiver/amp produce, and it is very subjective. I won't tell you that is the best amp, cause I have not heard them all, It's a great amp, IMO. I will say I love my 1500/m-60 combo. My 1500 drives the 8 ohm 60s with ease, and I am talking real loud if you desire. It does not even get hot, warm when it's dialed up. Like always, there are better amps, and a whole lot worse. The 2500 puts a bit more power and given that room (nice room) I can't see you wanting more. For what it's worth, I would not get caught up in the Yamaha YAPO auto set-up mike, do it manually, with a sound meter. The auto process sounds logical, but it's your room and your ear, you will get much better "personal" results tweaking it yourself, and it will take some tweaking, but worth it.
