Do you have a firewire connection? If so, I can confirm that M-Audio Firewire Audiophile does bit accurate captures. The software I used is Audacity (freeware). I use this setup because I have a macbook so an external sound card was my only option. The M-Audiophile 2496 PCI sound card can also capture bit perfect audio.
You only need a demodulator for AC3 captures. PCM audio is captured using a coaxial cable. No other gadgets required. Pretty sure DTS is also a direct capture.