Hello again,
Audacity has the ability to add top to your recordings once you have the track in the timeline. Got to effect / equalisation to see the eq window. Next drag the line up or down to add top do this nearer the 10kHz end. Click preview to hear what it sounds like and OK to apply to the recording. Beware of doing this on crappy pc speakers, they tend to have very poor bass response and tend to sound more toppy than proper hi fi speakers.
I'm assuming the original recordings sound good to begin with and that they only sound poor once transferred to the PC.