Need Sirius volume help!

I have a 2010 Tacoma Access Cab with a stock HU, non-JBL. Listen to Sirius almost exclusively. Never even put a CD in after over 8k miles. Now that the weather is warm I like to drive with the windows down. The problem is that even with the HU and Sirius unit maxed out I have a hard time hearing it. Here are some more details:

The Sirius is connected directly through the aux input.

Replaced the stock 6x9 front door speakers with Polk 6.5" 651's. It sounds better but not much louder.

I'm not concerned with having the highest quality sound. Don't think I have an ear that can tell the difference. Just want to make the volume loud and clear.

Don't need to be thumping on down the road either.

So now what do I do? Prefer to keep the factory HU(like the look) but would change it if that's the best move. Or is adding an amp the way to go? Don't want to spend an arm or a leg either.

Any suggestions/recommendations are appreciated!

 

Not sure but is it an after market Sirius or is it built in the head unit? I know that my XM had a setting for volume. Does the Sirius have that same feature?

 

The Sirius is aftermarket and the volume is turned all the way up.

 

it's just because our trucks are loud with the windows down. If you open the rear slider they get a lot quieter. If you add am amp to your speakers you can make them louder though