If sibilance is the main issue, try a dedicated de-esser... which is just a compressor keyed on frequency. I've gotten good use out of Voxengo Deft compressor in de-ess mode... there are certainly others to check out, like sonnox (mucho dinero!), fabfilter, toneboosters, etc.
RE: multi-band compression... one tool I've used for cleaning up/enhancing very old cassette recordings is Voxengo Soniformer, which really allows fine control of compression/expansion across the spectrum... basically multi-band compression on steroids. There are similar tools out there from other vendors. For example, it's a useful tool for zeroing in on noisy portions of the spectra, enhance those via upward compression, then follow with a noise filter dialed into taming the enhanced frequency ranges. "Normalizing" the bad frequencies allows the noise, click, whatever filters to not have to "dig into" the source so much, know what I mean?