Looking for digital noise filter recommendations

I am looking for noise filter software that will lower the noise floor before processing out to a sound card and it's digital outputs. I want software that runs the file through some sort of loop in ram before sending the signal out via a digital output to a dac.

I don't want anything that modifies the original data file.

Thanks for the recommendations.
Voyetra's audio Surgeon might do it - I am not absolutely sure though - download a free trial version here :