I'm kinda new to the plannar/magnepan world, but I am really interested in trying out a pair after all the reviews I've been reading. From what I understand these speakers are quite power hungry. What is the minimum I need to properly drive these? 
I currently have a VAC Avatar integrated tube amp. These are the stats:
Type: Integrated vacuum tube amplifier with MM phono stage and home theater (direct power amplifier) mode.
Tube Complement: two 12AX7 low noise (phono), two 12AX7 (line stage), three 12AU7/6189A (power amplifier), and four EL34 (power amplifier)
Options: Remote control for volume (motorized direct control) & mute
Power amplifier ("Home Theater" direct mode):
Output matching: 4 or 8 ohms nominal
Power output: 60 watts/channel ultra-linear; 27 watts/channel triode
Frequency response: 9 Hz - 35 kHz +0 / -0.5 dB, 3 Hz - 71 kHz +0 / -3.0 dB
Power bandwidth: 11 Hz - 63 kHz + 0 / -3.0 db ref. 50 watts
Gain: 25 dB ultra-linear; 23 dB triode
Residual noise: 1.5 mv at 8 ohm output
Channel separation: -72 dB @ 1 kHz; -60 dB @ 10 kHz
Line stage preamplifier:
Gain: 24 dB
Maximum input signal: Infinite (attenuation precedes line stage)
Noise contribution: Approx. 0.1 mv at power amplifier output 
THD contribution: Approx. 0.04% 
Tape output: Unity gain from selector, non-inverting 
Phono stage preamplifier: 
Gain: 37 dB (measured at tape output)
MC phono stage in place of the MM optional 
Residual noise: 3 mv at output (S/N ratio approx. 69 dB) 
Overload: 117 mv @ 1 kHz = 8 volts RMS output, 460 mv @ 10 kHz 
Frequency response: RIAA +/- 0.25 dB 
Notes: Does not invert absolute phase. 

Anyone know if these will do or if I'll have to upgrade? Love the tube sound . . . will I need to go solid state for Maggies? Thanks for putting up with the noobie question :) 

     The Magnepan 2.5R are 84db (the 3.7 are 86db and the 2.7 are 87db)..  I would consider all of these as inefficient speakers but not sufficiently so to rule out the use of the 60 watt Vac Avatar as long as the room isn't too large and the volume ismoderate. The speaker's 4 ohm impedance may be a bigger issue, however, the VAC does have 4 ohm  speaker taps.  I don't think we know enough about natureboy's room, budget or listening habits to rule out the use of his VAC.

    I think your suggestion of the Emerald Physics 100.2, (currently on sale for $599) may be a good match for the 2.5s.  I own a 100.2SE(150 watts/ch @ 4 ohms)  and use it in bridged mode(450 watts@ 4 ohms) for my CC3 center channel.  When I first received it I tried it out in stereo mode on my 2.7s (just out of curiosity) and it drove them very well; very good bass,  very dynamic,dead quiet and finely detailed  with a very sweet and smooth mid-range and treble.  It uses an analog power supply(not a switch mode power supply) and the amp is stable down to 2 ohms.  Of the 3 brands of class D amps I own, I think the Emerald Physics has the most tube-like mid-range and treble while still possessing the typical class D excellent bass response. 

    While I think this amp in stereo would perform very well driving Natureboy's 2.5s with its 100 watts/ch, I think buying 2 and bridging both to mono for 250 watts/ch is likely to give natureboy the best performance from his 2.5s, well worth the added expense.  


So both the  3.7s and the 1.7i would be upgrades to the 2.5's I'm looking at? I'm not quite a Magie expert, so input like this is definitely very valuable. If I can get a better speaker for a reasonable increase in price I can definitely look into it. 

I can start out by testing them with the avatar and if they are falling short, then I would switch out components. Class D was something I had not considered, but you are definitely making a strong case for them. Specially if I can get a tubey sound by preamp. I didn't know preamp dictated the sound as much as it seems to; I always thought amps would color your listening experience more than a preamp. 
I am listening in a rather large sized room (IMO)  . . it's a living room area with wood floors and it's about 650 sqft more or less. Maybe closer to 700. I have a pretty varied musical taste (as many people here tend to have), I tend to listen to a mix of classic rock, prog, jazz and classical. 
ok, I use a Sunfire Cinema Grand amp to drive my 1.5QRs...

The $$ allocation should likely be better speakers, then better amp.  The 3.7's are acoustically smaller than the 1.7's so why not consider those? (That is fresh and straight from the horse's mouth - may even be on their web site).

I'd love to have Bryston's too but they are not cheap - maybe the Canad. dollar will fall to 1% of where it is now...

A Maggie dealer near me is using a Rogue for drive but it is still $4k.  I'd say go for the 3.7s first and may do the same myself.
Nature boy, go read Harry Pearson's review of the 3.7's in Harry's Workshop, absolute sound and jonathan valins follow up's a good explanation of why the .7 variants are such a huge upgrade over past Maggie iterations......quasi ribbons have a LOT to do with it, the .7i's are yet another step beyond......I think you would see a night and day difference, and with amps, probably not.......