I'm glad rharv brought that up. softsynths are not going to work for compression or limiting going into the soundcard. they are ONLY after the fact.

you'll need a hardware compressor to compress/limit before the soundcard converters if that's what you want to do. Personally I do add a little hardware compression going in on vocals, but not much. it allows a smoother signal to work with when mixing.

but software VSTs are only after the signal has already been converted, so if you're clipping there, you can't fix it by normal means of a compressor/limiter. in fact, you can't really fix it at all except by special software to fix clipping, but honestly I don't like the artifacts those leave behind - I'd rather re-track the vocals with a better control on the gain in my signal chain.