Originally Posted by cheshirecat

Most BT channels on head units cut the low and emphasize mids, as they're calibrated to work with voices channeled through phone calls.

Is there any kind of setting on your unit relating to bluetooth that specifies which speakers are utilized or if they pass through any kind of filter?

My next suggestion would be to use an EQ program to bring up the bass on the BT channel.

Also, try different audio programs on the source unit.

Basically, you want to narrow down the issue. Most stuff I've seen related to bass quality over BT isn't the fault of BT itself, but of pre/post processing of the signal.