Hello Kyle,
The EP175 goes lower--within 3 dB to 32 Hz with useful output below 30 Hz--and produces greater overall output with ease, which you would expect from a bigger woofer in a larger enclosure with a more powerful amplifier.
If we look at low-frequency extension of instruments, the bottom key on a standard grand piano is at 28 Hz. Some pipe organs have pedal notes with a fundamental at 16 Hz, but the 2nd harmonic at 32 Hz is much stronger and the one we hear. Tuba and orchestral bass drum also extend into the 20-Hz region, and there are synthesizers with output at 20 Hz.
So I'd argue for getting the EP175 that has output below 30 Hz. Besides, should you move to a larger room, the EP175 can handle it without being overwhelmed. The EP125 couldn't keep up in a large space.
Use the speaker-level inputs to hook up the sub, running the speaker cables to the sub, then to the M3ti's. If you use a crossover frequency around 80 Hz or so--you'll have to experiment--you should be able to position the sub for the smoothest and deepest bass. Properly positioned, the EP175 has tight, musical bass that isn't boomy.
Regards,
