I think that you want to increase your input gain in Amplitube itself; use the Input knob just above the lock symbol at the bottom left. Also, you don't want your interface itself to clip; that will only yield an overloaded signal (in a bad way). Instead, let your clipping come from Amplitube itself.
If you increase the input gain in Amplitube, you can find a surprisingly great amount of gain without the use of OD pedals. I use a Les Paul too, and I just checked that on my presets I'm at 8.4dB on the Input Gain knob in Amplitube; that sets the gain staging just right for the high gain tones I love. I think that OD pedals are best when they color the tone the way you want. To me, these days you wouldn't want to use them just to increase the strength of the input to the amp; a clean boost can do the same thing without coloring your tone nearly as much (take a look at the Booster pedal from the Slash collection). I still would only use the Booster pedal if the Input knob wasn't enough. Mike Soldano said that modern amps should never need a pedal to have enough gain, and the Mark IV and Rectifiers certainly have enough on tap with the right amount of input gain! One other important point with the Rectifiers is that they do have a unique tone with regard to high gain pick attack; they feel softer. Even at extremely high gain, it can be looked at as a more refined tone, in a way. I had a friend who bought and returned both the Dual and Triple Recs early on because he could not accustom himself to the way those amps responded. As with any tone, it's a very personal thing. I feel, for a tone with really strong pick attack, the Mark IV is the way to go, just spend a LOT of time with the controls, and take a look at user manuals for the real amp online for guides on good tone settings as a basis to start.
Best of luck!
