Callista_Riff

Hi everybody. I have a 2011 Audi A6 3.0T that I have a AMI MMI to 3.5mm Aux cable that's plugged into a bluetooth receiver, Aukey BR-C8, so i can play music on my stereo via bluetooth.
It's pretty good for the most part. The only have two gripes with it.

The first is the loudness of it. I have the bass and subwoofers turned all the way up, and it sounds great at lower volume. But once you get past half of full volume, the bass can't keep up it seems and the treble will become very distorted most of the time
Is there any way to increase the loudness so they can stay in lockstep with the actual volume and sound cleaner without doing a bunch of rewiring and installing an amplifier and whatnot?

The second gripe is how easily the music distorts with treble at higher volumes. Most songs will do this, but not all. I was thinking it may be the audio codec quality or the quality of the bluetooth receiver, but i'm not sure if those are the only things.
To me, it seems like a high quality amplifier with audio cable might be able to solve the issue, but it's more involved than i'm willing to get with the audio system.

Is there anything that can take care of these two issues fairly easily?