Okay I Bought the Magnepan 3.6's

They are dealer demos, well broken-in... So, you don't think that a Pass X150.5 will do the job?

Yes, I will look at the Brystons too...

I don't think the 150.5 is enough, especially in your room. There is a reason so many are recommending huge amps like the Wyred for Sound, Bryston 14Bsst, or Pass 350.5. The maggies are not very efficient and will run through the 150.5's 300 watts in no time. Going to an amp like the Wyred for Sound or big Bryston will net you another 4-5 db's of headroom, a significant difference.

I like Pass stuff, but think it is extremely expensive and not worth twice as much as Bryston, with the 350.5 running nearly $12,000 for a new one, vs. the Bryston's still expensive $6,000. The Wyred for sound ST-1000 as the comparative bargain of $2000 gives you 1140 watts per side, a 6 db increase in output capability over the X150.5 amp. It also leaves a lot more cash in your pocked for other things.

Mcreyn,
what's your basis for writing that the X150.5 will not be sufficient power for the Maggie 3.6/Rs??

I took a look at the 3.6/R impedance curve in the S'phile review. Here is the link:
http://www.integracoustics.com/MUG/MUG/reviews/stereophile_mg36r.htm

scroll down to see the imp & phase plots.
What I see from these plots is that the speaker impedance & phase curves are quite well-behaved & that there isn't much phase shift across the audio band. We are talking +/- 35 degrees max w/ the phase being at 2.5KHz & higher. In the bass frequencies I see that the speaker is a relatively constant 5 Ohm load - very little phase shift in the bass freq.
So, IMO, a Pass X150.5 should be enough. My calc show that you will need about 40W/ch to produce 90dB SPL in your room sitting 10' away. The rest of the wattage will be for dynamics. My calculations show that you have 5dB of headroom for dynamics & I think that's quite good.
I do not know how much current the 150.5 can deliver but current delivery of the amp will have a bearing on how well the amp's wattage increases with decreasing speaker load. If the amp has enough current then you'll get 300W/ch into 4 Ohms & that appears to be sufficient for the 3.6/Rs in your room.
More wattage (along with current to support increase in wattage) is always better but it gets expensive on your wallet!

I recently used a Pass X350.5 with my Maggies, and the sound was great, but it did strain a little at volume, and was not quite on the same level overall with Maggies as the best amps I have used with them: Cary CAD 500 MB's, SandersSound Mono's, Brystons.

I think that next level up on the Pass (X600's) are probably better than any of these, from what I heard on my days with the X350.5's, but I would take any of these over the 350.5's right now.

Thanks for all the very interesting feedback, comments, and recommendations. My final analysis of the Mac 402 is that it is not the amp I want for my rig and my new 3'6's... I'll have to look elsewhere. Still leaning towards one of the Pass or possibly trying the Wyred 4 Sound ST-1000; in any case I am still looking!

If you happen to live in the Atlanta area and have one of these, please let me know.