Although I have not heard of anyone being able to set up their screen reader to tell them the percentage of each band of the equaliser in Winamp 2.x, you can make changes via the keyboard and listen to the results to see how you like it. First though, you'll need to open the graphical equaliser if it isn't open already. The 1 and 0 keys increase their respective band of the ten band equaliser. The row underneath decreases each band, from the q to the P keys. Similarly, the tilde and tab keys turn the pre-amp up and down respectively.
S opens the presets menu.
The A key toggles auto-loading of the equaliser.