I use the Amazing SlowDowner software to play CDs at a slower tempo for learning songs and to change keys for practicing songs in different keys. It will slow down, speed up, and change keys/pitch independently of each other function
It also has a built in eq to boost the bass and cut the other noise like banjos.
You can download a sample or trial version from
www.ronimusic.com.
A decent set of speakers with a sub-woofer for your computer is also very helpful.
Get of copy of some of the Flatt and Scruggs recordings from the late 50's early 60's era with Jake Tullock playing bass and crank it up.