Have you used Normalize to bring the peaks down to say -6 dB? That may make the problem a little less audible.
If the tracks have “flat topped” waveform, they have been recorded at excessive volume, causing “clipping”, where the tops of the waveform are lost because most digital recording equipment cannot capture sounds that are above 0 dB. Those songs are not fixable if the distortion sounds more than slight.
If there is a “tunnel effect”, it will be very hard to remove that. If it is reverberation, plug-ins to remove that are hard to make and usually cost a lot of money. See Mitigate overdose of reverb - #8 by Robert_J_H for a possible way to ameliorate the reverb using Audacity Noise Removal. But it may be better to see if there are other copies of the songs online.
If you are interested in pseudo stereo effects, also see How to turn mono into stereo other than just duplicating .
Gale