The sub when properly set up will better the mids and highs. It seems that yours is not set up properly....you shouldn't be aware that there is a sub operating.
Vinyl and subwoofers
I have a pair of Thiel 3.6 and a Thiel ss1 sub with the prescribed Thiel crossover. I have a pretty good vinyl rig with a Clearaudio performance se, Stradivari cartridge and a ARC PH8 phonostage. Although the Thiels go down to 20hz, an audiogon member persuaded me that I was missing something without a subwoofer. What I have heard with the Thiel SS1 sub and prescribed crossover is an amplification of record imperfections I was
not aware of without the sub. As well, the overall sound seems often muddied. Has anyone else had this problem with vinyl? Is this a problem with my setup? Any insights are very appreciated.