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 :) 
Though I am a Vandersteen fanboy, I do like the sound of Maggies.
+1 Ahendler, I too think 100 watts should be sufficient.
Here is a link to Atma-sphere and his endorsement for the Zero:
- it is on the right side of the page about mid-way down.
Much depends on what SPLs you enjoy. Your VAC will certainly drive Maggies, but- whether it will run out of steam, before reaching your preferred level, is another matter. An in-home audition is the only way to know for certain. Toting your VAC to a Magnepan dealer for an audition, will give you a good idea also. Then again, Magnepan offers in- home auditions on a couple models. They were actually paying people to try the 1.7i, in home and the MMg has a 60 day return policy:  btw: The size of your room and distance between the listening seat and speakers are also considerations, when discussing power requirement.
My VAC 30/30 was able to drive my Martin Logan SL-3's and Magnepan 1.6's and 1.7's at normal volumes in a medium size room. Your Avatar should have no problem. That said, I would highly recommend you listen to them first. I didn't care for either pair.
I have Magnepan 1.7s in a medium-sized room (about 350 sq ft).  I originally used a Linn Majik amp with 100 wpc @4 ohms.  The sound was plenty loud enough, but it just did not have enough dynamic punch.  I then changed to a Linn Klimax amp with 200 wpc @4ohms and got the dynamic punch that I was looking for.  In my view, 200 wpc is much better than 100 wpc.  I am very happy with 200 wpc and have not plans to add more power.
Nature Boy,

     I agree with gdnrbob, that Ralph (atmasphere) is probably the most knowledgeable about driving Magnepans with tube amps.  I know Maggies are all a relatively stable load of 4 ohms, only dipping slightly below this at certain frequencies. There are no crazy impedance dips like some electrostatics.  I also know there are many Maggie owners who drive  them with tube amps, although I think most use more than 40 watts.

     I own an older pair of 2.7QR Magnepans and have always driven them with high powered solid state amps,  my experience being the more power the better they performed.   initially I used a 400 watt class A/B amp and currently use 1,200 watt class D monoblcks.  The bass and dynamic range of my spkrs improved with the addition of more power.

    Another solution you may want to consider is pairing a good tube preamp with a solid state amp.  If you take this route, however, it's important you match the preamp's output impedance to the amp's input impedance, the general rule being the amp's input impedance should be at least 10 times the preamp's output impedance for best performance.  If you decide to use a class D amp, however, it's also very important you match the sound of the preamp to your personal sound preference since good class D amps are very neutral and your system' sound will be mainly dictated by the sound of your preamp and sources.

     Several Audiogon members have mentioned that Magnepan does not recommend using class D amps with their spkers.  This makes absolutely no sense to me because I have found them to be ideal for driving my panels. Class D amps are relatively inexpensive, very transparent, small, efficient, run cool and usually have plenty of power.  If you don't find a suitable tube amp at an affordable price, you might want to consider finding a tube preamp you like and match it to a good class D amp.  This hybrid approach will likely give you a tube sound without so many tubes to maintain and at a reduced cost.

Hope this helped a bit,