"I am recording Mono ~16 bits ~ 44.1kHz on my soundcard and the same levels in my software. I know my software is outdated too (Cool Edit Pro)
Output filter? Like a ground loop eliminator?" - Amethyste
A transformer type ground loop eliminator would likely be the first thing I'd try. They're inexpensive, available everywhere, and might help you in other recording scenarios. I've got one mounted in a plastic project case with a bunch of different I/O jacks peppering the sides. Really attenuates serial port noise and the like.
Cool Edit Pro (THE best sharware evar) was bought by Adobe and relabled / retooled into Audition. Adobe charges great gobs of money for it - the latest version actually guts much of the basic functionality that I use all the time for analysis, like the spectral pan and phase views. Anyway, you might try recording to 44.1kHz 32 bit float and then dithering down to 16 bits once you're done manipulating the track (normalizing, filtering, etc.) if Cool Edit has this option (I can't remember, though Audition does). Higher sampling rates like 96kHz and 192kHz might also be options if your hardware and software support it. Cool Edit can probably downsample the sample rate to 44.1kHz and dither the float to 16 bits. At any rate, try to get the lowest noise floor you can (the ground loop eliminator might help for that) along with the hottest signal you can without clipping. You can maybe watch the VU meters in Cool Edit to see these things.