If you feel the better video processor of the 906 isn't necessary then you got a good deal. The 4308 is a proven performer and the GUI is a very nice thing to have along with the wi-fi, one less wire to run, and the new features, you should feel very happy to have bought a great product for an excellent price.
I wouldn't put too much into the THX certification, I am quite certain if Denon wanted to spend the money for THX certification on their models other than the 5300 series, they would easily attain the same certifications.
