Amp newbie? Adcom GFA-555 vs Mcintosh 2505


Hi I'm definitely a newbie, and already know my initial choices in starting my first adult sound system will make experienced folks around here cringe...but I'm wondering if I might still garnish a bit of insight to help reduce additional "bad" choices or steepen the learning curve just a bit.

From the beginning; I went and auditioned speakers at Best Buy, and of course fell in love with Martin Logans...and decided to order a pair of Magnepan MMGs (not a bad start right?). Did some research and bought a HK3490, maybe not the wisest choice...kind of wish I had started with separates...but it should be able to handle the MMGs...I know I amjumping the gun a little because I have not even heard this combo due to some shipping issues with Magnepan...but my question is this...I'm thinking I can use the HK3490 as my preamp and add a separate amp?

And the real question how do you compare amps...I am looking at a few intro. affordability choices like the Adcom GFA-555 rated at 200w/channel vs. the Mcintosh 2505 rated at 50w/channel...but I'm under the belief it's not just the watts, but the amps that are driving them...otherwise my HK3490 at 120w/channel should have the juice to power the maggies...so how do I know which will deliver a better sound for the buck...and more importantly...how many watts do I really need?
windhorze
Wind - I'm a relative newbie driving MMGs with a 200w (360w into 4 ohms) ss power amp. I think mine (a B&K) does the job well (smooth, warm sound) but haven't done the comparisons to have an informed opinion. I took a similar route as you with preamps and began by using the preamp output of a Rotel integrated. I am happy to have an e-mail discussion about this since we are in a similar boat, but 2 comments: 1) the preamp selection is very, very important; 2) MMGs are great. You are going to love them long time.
Thank all for your responses so far....as far as some additional concerns... Drumhead- HK3490 is rated at 120 wpc at 8 ohms, and only 150 wpc at 4 ohms, this was my first concern (although their literature says it is stable at 4 ohms)...and Bwp- yes, I am already eyeing some of the used 1.6's around here...and yes the final concern...I have a slightly addictive personality and I see potential problems down the road...is there an audiophile 12 step program in the LA area by any chance? ;-) I might need an intervention!
Windhorze

Power ratings of receivers won’t usually double when imp is halved… as some other amps will. That doubling down aspect is no reason to reject an amp either.

RE Audio 12 step

First things first…. Place a greater priority on what you have, rather than what you desire. It’ll always work itself out. Always. One day at a time.

Turning off the personal confuser and listening to your system will help immensely too.
I wouldn't push the volume too much on the HK. It only consumes 310 watts max.That sounds like they may be giving it a higher power rating than it can really give out.Be careful until you get a quality power amp capable of driving 4 ohm loads all the time.Maybe start a new thread asking for the best sounding lower price amp to buy for the Magnepans.Stating a price limit will help too.