Most DJ/mixing programs have some sort of gain scanning utility built into them. Even most ripping & encoding programs have some form of gain scanning or normalization effects built into them or available as a plugin. For instance, ripping audio only files to WAV or FLAC, I like using CDex. For recording non-CD media, Adobe AUdition is my tool of choice.
PCMCIA sound cards that are at least 24-bit and have multiple I/O ports will do nicely - there are quite a few to chose from.
I'm not that familiar with Traktor, but I do know that Virtual DJ will do gain and BPM scans on every sort of audio, video and karaoke file. Same thing with Tricerasoft Swift Elite.
The term Computerized Performance System or CPS is a bit more than a buzz-word, it is a widely used term in the industry with the Computer DJ Summit, me in all the books and articles I write, the ADJA, Denon, Tricerasoft, etc.