Bluetooth usually uses resampling and a lossy codec to transfer audio between the source (your PC) and the receiver (the headphones). So even if you start with hi-res audio (24/192 PCM, for example) you'll end up listening to 44.1 AAC.
You'd probably get better sound quality by buying an external DAC and headphone amp and switching to quality wired headphones. The DAC attaches to your computer via USB and then the amp is connected to the analog outputs of the DAC. An example would be to buy the JDS Labs Atom DAC+ ($109) and pair it with the Atom Amp+ ($99). For wired headphones, I highly recommend the AKG K371 ($145).