See if the following thread helps at all

by Pepe7 - 11/14/13 8:05 AM

In Reply to: Question about Bose Acoustimass 600 & Pioneer by diannenet

http://www.avsforum.com/t/675030/understanding-lfe-attenuator-setting-on-pioneer-recevier

The biggest issue for me is, the Bose isn't actually a true subwoofer but in reality, a bass module. So you might have to futz with a few things on receivers like the Pio, etc.

Have you also run through the other settings for various speaker types? I see the important stuff on p.30 on the manual here:
http://www.pioneerelectronics.com/StaticFiles/Manuals/Home/VSX-522-K_OperatingInstructions070312.pdf

Also, have you tried the 'plus' setting, mentioned on p.31/left column?