I purchased a used SVS Bass Interface Box about six months ago from a member of this forum. It added punch, phase control and a subsonic filter to my dual CS+ 20-39 subs driven by a Samson S1000. I split the LFE signal to another amp driving 6 bass shakers. The addition of the SVS interface helped drive the Samson S1000 and second amp (a Rotel 980BX) easily to reference levels. The SVS Bass Interface Box also introduced some hum that was not present without it. After trying the usual approaches (e.g., lifting the ground to the Samson amp, improving cable TV ground, using a ground isolator on cable) to eliminate the hum without success, I sent a note to SVS seeking advice. Without hesitation Tom V. offered to exchange my second-hand SVS Bass Interface Box for the current improved version at no charge. The new SVS Bass interface is now in my system. It represents a significant improvement over the previous version. For those reluctant to purchase products over the internet, be assured that SVS will go the extra mile to ensure customer satisfaction.