Just an update...
Still farting around with the M9. So far here's my grading of the various effects:
Compressors: A
They sound great and are very quiet. They add practically no noise even we set really high. Tube compressor is my favorite. Very transparent and natural sounding.
Distortions, Overdrives and Fuzzes: C+ to B-
They sound OK. The EQing on them is finicky, and they sound a bit thin and flat compared to analog pedals and especically comprared to a tube amp. They lack the harmonic complexity of the true circuits and are less responsive to pick attack and volume control changes. Tubescreamer model has a bit of a pumping and breathing thing going on the clipped part of the tone that is a bit odd. It's more noticable into a clean channel. The big muff model is OK and the tube drive model is very tube like.
Choruses: A
Great analog sounding swirl with great clarity and definition. Not muddy sounding like some real analog choruses can get. Lots of options and textures to pick from.
Phasers: A
Again, great analog sound with clarity and definition. Script Phase 90 model is spot on. I wish there was a EH Small Stone model in there though.
Flangers: A
Sound great like the chorues. Very analog sounding and clear. Lots of options here too.
Rotary: A
Sounds like a leslie to me. Especially with a bit of breakup. I wish it had actually speed settings instead of just fast and slow switch like a real leslie, but otherwise sounds great. An adjustable ramp time would be nice too.
Delays: A
All of them sound great. I really like the analog w/ mod (Deluxe Memory Man) model. Very nice textures.
Reverb: A
I have the verbzilla pedal and this has all the same great verb tones in it. Hall and plate verbs are fantastic. '63 Spring is pretty good, but the real unit is sweeter sounding.
Wahs: C
Very harsh and peaky sounding. I found most of them unusable with high gain as it just made for pronounced harmonic squalking on top of my playing. There's no sweet, warm Voodoo Child tone in here. There's no adjustability in any of the wahs, which is a shame.
Univibe: B+
Real univibes vary quite a bit, so it's hard to say if it's a good copy or not, but it does sound pretty darn good with some tweaking. I was able to get a machine gun and bridge of sighs thing going pretty easily.
Harmonizer: B
It does it jobs prety well, but doesn't track as well as some. My old G Force had a far better harmonizer in it.
Whammy: A
They did a pretty good job capturing the Digitech Whammy here. With a good expression pedal, it's great.
Overall, I'm still quite impressed. Like the vast majority of modeling products, it falls short when it comes to gain effects. Digital modeling has yet to fully capture the harmonic complexity and varying frequency response of analog and tube distortion. For now I'll stick with my true bypass, analog tubescreamer clone and a real analog wah pedal. The modulation, delay, and reverb effects are all fantastic. This is where digital modeling really shines. You can get all the great effects without the irritating noise of many of the originals. The M9 is quiet and transparent enough to work well in front of amps, but for me most of the effects sound better in the loop. Switching between its true bypass and dsp bypass modes, I could tell no difference in tone with all of the effects modules bypassed. The unit is very quiet. The tuner works quite well, so my Planet Waves tuner will off to eBay soon. I'm still considering upgrading to the M13 for 4 effects at once and 12 scenes on deck, but I probably would not be using with the four cable method. While the compressors might be nice in front of my amp, they are quiet enough to work in the effects loop just as well. Even without the gain and wah effects, the M9 is worth every penny just for the choruses, delays, and reverbs. The looper is fantastic too. It's way more flexible than the looper in my Boss DD-7. I really like the way it blurs the lines between old fashioned pedals and a programmable processor. You get the best of both worlds and can use it either way. Add a mini amp gizmo for channel switching and you get one button preset changes with amp control. Very nice indeed.