Seems like samplerate mismatch - video sound samplerate is typically 48khz, you might be recording your audio at 44,1khz.
Converting the audio file could fix the problem, however I have had some issues with that.
Try to isolate the ground from power cables going into Genelecs. I don't know which type power connectors do you have, but for those eu ones I've found that taping these bronze connectors with duct tape or even cutting them off helps.
I hate the sound of hd280, but they have great isolation... usually go-to headphones for drummers. Singers, guitarists and others will have Sony mdr-7506 or Beyerdynamic 770 phones - less isolation but better sound. Can't tell you about ATH-M50 but I'm interested hearing them.
Maybe you could tell us more about your processor (right click on my computer->properties)? 2ghz doesn't tell much these days, it's all about the cores now.
Okay... let's start with basic things:
Are you using XLR to XLR cable?
Is the phantom power turned on?
Can you get the Clip led to light up? (just to see if signal makes it to M-Audio)
Input selector on "Front"?
Is the adapter connected or are you running only on firewire power?
Why asio4all...
I did a small transient designer shootout for myself some time ago. I didn't like transient monster at all. For me, it's between SPL Transient designer and Bittersweer. Bittersweet is great, but no release knob. Then again Bittersweet has M/S processing option. :)
First, duplicating a track will not cause any phase issues - it's a identical copy. Now if you move one track slightly off time then you start to have issues.
Your idea is basically good, but I wouldn't add any distortion since it could turn your guitar track into a truckload of mud pretty...
First the hiss issue - have you switched on phantom power?
Secondly the echo - are you monitoring thru speakers? That could cause a loop between the mic and the speakers.
Post a sample if you can.
1) Unless you want to buy the rack version of autotune you have to stick with plugins. If you are getting too much latency you will have to turn down the buffer size to acceptable level. If it starts to making crackling sounds, then your computer is probably too slow to handle it.
Really, does...
1) Forget the foam, forget the egg cartons. Since you can't put treatment on walls you can make some moveable treating walls that sit on the ground. Something like that:
http://advancedacoustics.files.wordpress.com/2013/02/2013-02-20-14-41-27.jpg
The simplest thing would be building frame from...
Usually if there are any special drivers you will find these on manufacturers website. Of course check before buying if the device is Windows 7 compatible.
Check out various transient shapers, for example google for Flux Bittersweet which is free. It will get rid of the transients on cymbials... but also on everything else you have on overheads so you got to try and find a good balance.