Thanks to everyone for your help!
First, I reduced the level on the center channel and fronts to +2.0 dB and +5.0 dB, respectively. I left the crossover at 80 Hz. That seems to have made a big difference. The bass seems much stronger and deeper now, as I originally hoped for. I also checked the bass and treble settings for the receiver's equalizer. Bass is set to +2 dB, and treble is 0.
Currently, the sub is on the left side of my entertainment center, close to the corner of the room. I can try moving it around, but the PSW125 is rather large, so it's tough to hide. Don't think I'll have many options there.
Another point of note... on the receiver's HDMI menu, there is a setting called "SW LEVEL". It has three settings: AUTO, 0 dB, or +10 dB. It was set to 0 dB, and I changed it to Auto. I don't know if that was part of the problem, but I guess I'll leave it at Auto, since the sound is much deeper now.
One other (somewhat related) question... both my HD set top box and blu-ray player are using an optical audio cable, in addition to the HDMI for video. When our cable tech came out to install the HD box, he recommended using optical audio, if possible, because it doesn't suffer from EMI. Overall, can I expect noticeably better sound over the optical or coaxial audio cable vs. HDMI? Is it worth the extra cable connections, or am I just as well off having the audio come through the HDMI cables?
Oh, and I'm new to this stuff... what's "pink noise"?
Again, thanks for all the help and advice!