Mono vs Mono + Amplitube

If I choose a mono input in Sonar, by default Amplitube will process that input as mono and at Amplitubes input stage I will only see the left signal. If I choose a mono input in Reaper, Amplitube will process that input in a "dual mono??" fashion which makes the signal a lot louder and I will see both left and right signal in Amplitube's input meter. Now I understand how you'd want to hear a mono signal in both speakers, but shouldn't it only do that at the output? The fact that the mono signal is being processed in this way for some reason makes Amplitube clip/distort on my clean presets even when Amplitube's input meters are very low. Basically, my issue is with Amplitube. I get distortion on clean presets even when I'm nowhere near the red in Amplitube's input meter when both the L+R meters are going. Is there something I can do in Reaper that would be the equivilent of Sonar's "Enable mono processing" option to force Amplitube to only show L or R at the input stage?

Thanks for the replies. I'm not the best at explaining things. Though I try. Basically, If I can get only one side of audio showing up in Amplitube's input meter and be able to record a mono signal on that same track. I'm set. If Amplitube's input meter shows signal from both L and R then it boosts the live signal too much.. In the real world it almost seems like if you had two outputs on your electric guitar and you plugged them both into one amp, hence boosting your signal when you don't want it boosted. Maybe there's some issue with my setup.. Not sure.. I just know that everything sounds great as long as only the left input signal is showing up in Amplitube.

I know what you mean, but to me you should be able to have the one input (the double mono we'll say) I hate to ask all the same ol' cliche questions but is it possible the soundcard level is too hot?

certainly, if there is something I can do to help, just let me know :)