Dallas_burn: if by composite audio you just mean stereo L/R RCA jacks, then use the CD/TAPE Outputs (the top two terminals), as indicated on page 17 of the manual "Connecting other audio components". For the Subwoofer, you can either just connect the Subwoofer out to the "L" or "R" channel and turn the gain up, or use a Y-adapter/splitter from Radio Shack to split your single Subwoofer output to two outputs.
Now my questions
I just bought my VSX-521-K on a black friday deal. This is my first experience with the MCACC feature and so far I think I'm pleased with the results after running it, but I'd really like some way to see the results of the tuning such as the EQ and possibly the phase adjustments. The 521 does not have the "advanced MCACC", just the "yes" (basic?) version. The on screen display doesn't seem to give me any more information than just using the receiver display, am I missing something, is there somewhere I can get a little more information about the MCACC calibration?
Also, kind of related to the above question, the specs on the Pioneer list a "Symmetric EQ" feature. What exactly is that? I can't find any literature on that feature... and I'm trying to figure out what a "Symmetric" equalizer could possibly be.
edit: nevermind on the second question, finally dug up some information. Basically means the speaker pairs (front L/R, rear L/R, etc) are equalized (tuned) identically, because they assume they are the same speaker type, to keep the system from adjusting your L speaker different than the R.
"The Symmetric EQ (Equaliser) is a left and right symmetrical acoustic equaliser which delivers enhanced stereo accuracy.
The default Symmetry setting implements symmetric correction for each pair of speakers to flatten the frequency-amplitude characteristics"