Nothing wrong with increasing the level after running Audyssey. Many people do it and you may have heard the term about running the sub "hot".
However, it would be useful if you had something like a SPL meter to let you know how hot you are running the sub. For example, you might have been running your Mirage hotter than the SVS, that's why it sounded louder to you.
I am in the process of letting it 'break in' and will critique it a little more after that. I do want to like this sub, trust me I do! I am just wondering if maybe I got a (dare I say it) defective sub? My thought with that though is that I have not read anything about quality issues with these, I have just read outstanding reviews.
I know how you feel. Just spent a wad of cash for an upgrade and having big expectations of being blown away... but not getting it.
As with all manufactured goods, there is a slight possibility of defects. Unlikely, but not impossible. Again here's where an SPL meter might be useful since it can help measure the sub's output to see if it is in line with expectation. I guess for the moment, just let the SVS break in then listen again. Do try repositioning the sub if necessary.