I recently had a amp failure on one of my Hsu ULS-15 subwoofers that I bought back in April 2009.
Anyhow I need to give out a huge shout out to the ppl at Hsu Research for their Tech (Leo) and customer support (Kevin). My first email to Tech support was sent on a Saturday morning and I received a reply that afternoon. I had a follow up question on Sunday morning and again got a reply that afternoon. These days you just don't expect replies to emails during the weekend. I sent in the amp last Wednesday and it was return to me yesterday. So a 6 day turnaround with shipping is awesome. Plus they were kind enough to give me a discount even though the amp was way past it's warranty. I do plan on keeping them in mind for any other subs I might need.