On most of my stuff, I have "audio boost" on. Its seems to add just a little bit more volume.
In the house, the 500 is well enough, but I do run it though an external speaker (paper clip trick until warranty expires) which yields better fidelity.
In the truck, I have an after market stereo, which has multiple rear inputs (ipod, 3 1/8" jacks, etc). I run the 500 through the head unit, and that really brings out the full potential of the radio. The audio is sweet, and digital REALLY sounds crisp and full with this setup.
Sad to say, the radio IS capable of full, well rounded sound, but once again, the mfrs cut corners with case/speaker/audio amp combination. Common among consumer grade portable scanners.
One trick I also have: I modified an old Motorola STX speaker mic to get some more oomph while portable.
I rambled, but hope this helps somewhat.
Rich