I don't have the BC23A, though I've thought about getting one...but every set of computer speakers I ever connected to the headphone jack of an HH scanner would literally blast. That is with the scanner volume set to about half. Many are designed to tap 12VDC from the computer to operate...these can easily be used in a mobile install, either both or just the "master" speaker that contains the amp & inputs. Just FYI I have some hearing loss and tinnitus due to exposure to loud equipment in years past and I have little to no trouble hearing/understanding traffic via amplified computer speakers.I'm having the same trouble - I have excellent hearing and a relatively quiet vehicle, and the radio is just plain not loud enough.
So I bought a Uniden BC23A. And it's made maybe a 10% improvement, if that. Now it gets louder, but when it reaches about the level that the radio by itself was maxxing out on, it starts to distort. It will get louder after that, but it's a useless, distorted louder. I've turned the level on the speaker down a bit and that might have given me a slightly larger useful window, but all in all it's really disappointing. Makes a lot of traffic hard if not impossible to understand. The only traffic that's loud/easy to copy is P25 phase 2 - it's VERY loud.
I've got a Kenwood V71a dual band ham rig in the truck as well with a small CB-type speaker, and the difference is incredible. It's extremely easy to understand and it can crank REALLY loud.
If anybody has any ideas/solutions I would be very grateful.