Dunno about your specific situation, but SoundForge has a nice plug-in you might want to check out called Express FX Audio Restoration that worked wonders with one tape that I had that also had a lot of hiss after normalizing.
I stopped using those automated de-hiss tools probably back in the 90's. They do a lot more harm than good, they create a small sort of underwater-sounding, crystal-y type audio effect. It's slight, and isn't noticable on all audio systems, but it's there. If you hear it once on a given recording or a given playback system then it's usually enough to pick it out on other recordings and other playback systems, and is probably enough to never want to do it again. I would just use slight EQ to get rid of hiss, which in my opinion works better anyway.
To the original poster, yes, posting a short wav clip of your set might help. Some users might give it a shot and post back a sample of their results, which I've seen around here from time to time. If it works out alright, they might post the specific settings they used so you can replicate it.
If you say you can actually boost the volume and not hear any hiss on playback, then 'export' to a wav file with the same volume and all of a sudden the hiss appears out of nowhere, even though the volume isn't changing from the previous playback, then yes that would be quite strange. I can't imagine that's the case, but if so, play it back when the volume is already raised and it doesn't have hiss, and try using the windows "what you hear" setting to record a clip to a seperate wav file. Then save your original one when the hiss gets added, and you'll have 2 files; compare that against the 'what you hear' wav clip which is after boosting but before exporting, and if they're really both at the same volume, one with hiss and one without, then you know there's a problem that occurs when you export to a new file. I would guess you're mistaken and the hiss gets added after any initial volume boosting, not just from simply exporting/saving, but maybe it's worth a try.