Pre amp out on Pass Labs INT-150

Recently purchased a Pass Labs INT-150 and connected an SVS SB-13 Ultra (with SVS Ultra bookshelves) to the preamp outs (RCA). Setup the low pass filter on the sub, high pass disabled. Started playing some music and noticed bass response was negligible (mids and highs were just fine). I ran some frequency sweep files and it seems frequencies below ~100 hz are not being output for some reason. Reconnected an older integrated amp to and everything seems fine. Is this an equipment matching issue or amp itself? I'm stumped.

Anyone else had this issue? Any feedback or input would be greatly appreciated. Thanks in advance.

Tim