Nice Result

I adjusted the crossover point on my subwoofer to the rolloff point of my mains, making my system sound much better planned and at least $80 more expensive.

My subwoofer, being a long-excursion driver, is rather sloppy at transients (and turns the "p" sound into "ppp"), and since my mains are always going to be quicker at bass than my subwoofer, taking advantage of that speed was one of the best things I've ever done with my system.

Is there something I can do to make my subwoofer less boomy?
It's a Blueprint 1001 10" woofer in a 2 cu. ft. vented box (vented to the outside with a high-flow 12"x1" rectangular port) powered by a 120w parts express amplifier and with a bass cutoff (f3) of 25 Hz. It's a nice unit, great for home theater boom (it positively roars through action movies), but I'm looking for a way to make it more accurate for when I'm listening to music.

It's in the corner, sitting on the floor (no spikes), and yes, my amp does support phase adjustment in the form of a switch between 0 and 180 degrees. Oh, and yeah, it's crossed over at about 70 Hz. My mains have an f3 of 60 hz and an f0 of 65 Hz. My mains used to be Fried Q's but I had to replace the aging drivers with Pioneers, as dictated by my finances.
Ok, few possibilites:

1) Fiddle with the phase switch. Mine is offset about 60 degrees. This can make a big difference.

2) Move the sub out of the corner. Corner positioning without EQ can have its downsides.

3) Spike it, definitely. The way the sub is coupled with the floor can make a huge difference.

4) Plug the port (wad of socks works nicely). It raises your f3, but allows it to act as a sealed sub.

5) I'm assuming that the PE amp has that built in bass boost. Look into disabling this (I believe its a matter of changing resistors on the newer amps). Often, when the boost kicks in, you can get an annoying thump sound that can make it sound boomy. This was the primary reason I went with Adire's amp over PE's with similar power output.

6) All too often overlooked: the cable/connectors. After changing my subwoofer interconnects from el cheapo temp cables to higher quality diy ones, the bass tightened up considerably. Also consider using high quality connectors and internal wiring for the subs (Silver Sonic speaker wire works nicely here, and I've had positive results with my own braided litzwire as well.)

Edit: Also considering increasing the mass/weight on top of your sub to better couple it to the floor. A bag of sand on top can work nicely. Also, if the sub is on carpet, try placing either a piece of granite, marble, concrete, or even MDF under it. This works well too.