Greetings Chris and welcome.
That low level issue is not related to the bit rates. It's common to have low levels on an export even though it sounds nice and up to level in the MC6 program.
That is what mastering is all about. Taking that mixed, but lower level file and getting the EQ, compression, and levels up to what most consider to be "radio ready" standards and levels.
I would suggest that you learn about that process and work on it. If I could say do this or do that and waaa laaa, the problem is solved, that would be cool but it's a learning process that you have to go through.
Go to this link:
http://www.izotope.com/products/audio/ozone/support.asp and get the free PDF guides and study them. I said there wasn't a do this or do that sort of thing but perhaps there is....sort of... many folks here including me, use Ozone as a finish to our mixes:
http://www.izotope.com/products/audio/ozone/download.asp it has a free 10 day functioning demo available for you to try. That learning process applies even using Ozone. You should understand what it's actually doing in order to get the best results.
hope this helps