Bit-perfect means that a pure digital signal is sent out by the soundcard to the DAC. it basically refers to how the driver software for the soundcard handles the information.
With windows, if you are using "waveout" or "directsound" settings, the sound goes through a thing called Kmixer which is like a junction box for handling all PC sounds. This may or may not have a negative impact. Other soundcards automatically upsample your audio from 44.1 to 48 khz whether you like it or not.
Bit-perfect, in the PC context, basically means avoiding using driver or playback settings that avoid kmixer and automatic upsampling. Hence your data is sent straight through to the DAC without any additional messing by windows or the drivers.
In foobar there is a setting called kernal streaming. Otherwise there are soundcards that support ASIO. These are "bit perfect" alternatives to waveout and directsound.
It seems the cheapest way to get bit perfect (via optical Toslink) is the Chaintech AV710 card, cost $26. You will find guides here on how to set it up correctly.
Other than that, a search here on "bit perfect" will keep you busy looking at other models, internal and external.
DAC's will convert the signal whether it's bit-perfect or not, unless the DAC is limited to handling a 44.1 input and your card upsamples to 48. The whole bit-perfect thing is not about the DAC, its about the software side of things.
hope that makes sense.