The right amp for my system

if the pioneer isnt up to the task, then the marantz probably wont do it either. You need to step it up to something in the realm of an Anthem at 200wpc. The Pioneer is a nice unit but when you put that much in one box, it does have it limitations as you've seen.

I have a 130w Pioneer Elite. I drive the center and rears with the Pioneer, thus preserving all the functionality of the receiver, including driving ceiling speakers in other rooms with channels 6 & 7. I inserted a Wyred for sound STI 500 integrated with a home theater bypass for 2 channel. Before that, I used the Pioneer as a pre-amp and ran it through a Rotel 1095 for 5 channel amp. Sounded great, and was less complicated for the wife and kids to use for movies. You could probably talk me into selling the 1095 if your interested.

Martin Logans are tough to drive, with a wild impedance curve. No receiver is going to drive them properly.

You are likely looking at a good 150 - 200wpc dedicated power amp with lots of current. You could use the Pioneer as a pre, but once you've invested in the power, you will likely find the pre lacking.

If you like the speakers, save up a bit and go for a decent pre/pro, power combo.

Previous comments are correct. If I understand correctly this is a 3 channel theatre system. Might consider the Odyssey HT-3 three channel which will provide enough current as suggested AND proper damping factor to control the panels which is oft overlooked.

What is your source? I was in about the same boat as you describe. I had Marantz 125wpc receiver driving Focal 918s with an old Pioneer multidisc changer.
This year I bought a rebuilt older H/K Citation 16a that is rated 150wpc. The amp made quite a difference in overall sound for the $ spent.
I recently bought a Sony 5400 cd player and it made a huge difference. My system was very tiring to listen to with the Marantz because I would have to turn it up so loud to get certain sounds and then as different aspects of the song would kick in it would be complete overkill...just loud! The Sony seemed to level things out and decrease my desire to always turn it up.

With that being said I would shop around and buy an amp you can afford...then go from there. I am looking at preamps now for 2 channel setup. I have stopped using my center channel speaker since I got the Sony. It sounds best in the pure direct mode.