I decided to give one of my classical recordings (a binaural recording of an a cappella chorale) the parallel compression treatment tonight. Even though I felt a bit squicked about applying compression to a live recording, the result was very pleasing. It sounded as if I had moved up right up to the front row! Details that seemed slightly hazy in the original leaped into clarity, and the remastered version has a lot more punch to it without seeming to lose the dynamics. Of course, to be pedantic, it does lose some dynamic range, but this is not the sort of Death Magnetic-style brickwalling that I hate. All in all, it was well worth the fiddling (and yes, this is a fiddly process - it took a lot of fiddling to keep the compressor from pumping).
In Audacity, I came up with -13 dB threshold, -45 dB noise floor, 6.5:1 compression ratio, 0.2 sec attack time, and 10 sec decay time for the compressed track, and then I set the compressed track -5 dB below the uncompressed track. Then, I knocked back the gain on both tracks until there was no more clipping at the peaks, and mixed them together.
I'm going to have to try this on some of my other pulls now...