Hi,
I need two information:
I'm gonna shoot a video with a sennheiser mka60,
how good is the 7d audio compression?
Is there a way to have an av out and the lcd active at the same time?
Thank you in advance for the answers :-)
Marco.

The 7D's audio compression is pretty good, but what is going to get you is the Auto Gain Control in the camera that can not be turned off. (it can be tricked, though not the best solution) Your best best is to get an external recorder like the HN4 (do a search) and sync in post.

Thank you :-)
and what about the video out? It is possible to have the camera lcd active and simoultanosely a video out on another monitor?

When you take a video out from the A/V port, you can't use the LCD screen. The act of plugging in the cable disables the LCD. Maybe they'll have a firmware fix for that someday.