The PS 312 appears to be a slight step up from the JBL PB12.
Both JBL and Infinity have had serious subwoofer amplifier difficulties (the JBL L8400P is an exception). You should not consider a second-hand model. I have a PB12 that I use in a HT system with another subwoofer but not in my main two systems that use larger subwoofers. You might consider what is listed below.
Two of the recommended subs ~$400 are the Hsu STF-2 and eD A2-300 that do not show some of the deficiencies of lesser-priced recommended subs (i.e., one note wonders or little output below 30 Hz).http://www.hometheaterforum.com/foru...er-test-review
- STF-2 review by Ed Mullen