Rdelpozo, if each sub isn't calibrated,then meaningful comparisons are almost impossible. Say you set the volume knob on each sub at 50%, but the STF-2 is louder at that setting than the EP175. Almost any sub will sound boomy or abnormal if turned up too loud.

Calibration is very easy. The easiest way is using your receiver's pink noise test tones. You just switch from speaker to speaker while playing pink noise, and make sure the meter reads about the same from each speaker, including the subwoofer. Typical levels to calibrate to are 70, 75 or 80db. For 70db, set the meter on "C" weighting, slow response, 70db scale. When the dial says 0db, you're reading 70db sound. For 75db, use the 70db scale and the needle will reach +5db (75 = 70+5).

Adjust your master volume to about the right level to hit 70 or 75db. The receiver or DVD test tones will usually switch from speaker to speaker automatically. When on the subwoofer, if it reads too low, turn up the subwoofer volume knob. If too high, turn it down.

That said, some people like a little more bass. It's perfectly OK for your sub to be (say) 3db louder than your other speakers, if that's your taste. Just make sure you set both subs to the same +3db point.

Don't point the meter at each speaker. Hold it roughly straight up.

Using tones from the DVD is better because it incorporates the entire playback chain. However most test DVDs have many different test tones for varying purposes. For example, low frequency sweeps to check for room rattles, etc. For your immediate purposes you don't need those.

What you want is a basic subwoofer level calibration so that both EP175 and STF-2 are set properly with respect to your other speakers. Pink noise is the best for that. It only takes a minute once you get the hang of it.

Calibrate the EP175, do some basic listening tests. Then hook up and calibrate the STF-2 and repeat the listening tests. My guess is they'll sound much more similar after doing the calibration.

I'm interested in how much difference you can hear between them after both are calibrated.