I have never heard the EP350, but I own and enjoy the STF-2. It's difficult for me to compare it to other subs, because I haven't heard a lot of others. All I know is that it is far superior to the JBL PB-10 I was using until the HSU cometh.
The STF-2 provides much tighter (less boomier) bass, with excellent transient response (how quickly the driver recovers after sounding a note). So, I'm very happy with my STF-2.
My room is 11.5'W x 18'L x 8' high, and opens into a 10' x 10' x 8' dining area. That totals up to around 2450 cubic feet (1656 cu. ft. living area; 800 cu. ft. dining area. The STF-2 handles that much space just fine.
