I just helped my Brother-in-law hook up his 3rd SVS 25-31PC+. The first two were purchased about 3 years ago. The last one was purchased about 3 weeks ago. All subs positioned together. The interesting thing is that we had to run the phase 180 degrees out with the new sub. I think the new sub has an improved woofer...but the phase reversal is interesting. Anyone experience this? Also the new subs surround feels different when compared to the older subs...not as firm? Still sound great....!