Using A/V receiver as pre-amp?

I'm new to hifi and still looking for a pre-amp. I was told to use my current A/V receiver as pre-amp temporarily. Does this really work? BTW, I've just bought a used Bryston 4B ST and a pair of Thiel CS3.5

Yeah it will work temporarily or permanently for that matter. But your system will sound markedly better when you get a bonafide preamp for music (unless you have one helluva an AV receiver). Use the receiver for a while, so you can really take your time and get the preamp that you will be really happy with for a long while. It's murder trying to get your money back from experiments. With your nice speakers and poweramp, you're going to want to get a quality pre to match.

Good luck.
It works if the receiver has pre-outs -- most do. Given the quality of your speakers and power amp, and assuming your receiver analog section isn't of the same quality, I'd suggest that you get a stand alone stereo pre-amp with stereo-bypass.
Don't skimp on your preamp. It's more important to the sound than a newbie would first expect. You might consider buying an old but very good 2 channel preamp which has depreciated to a stable plataeu and could be resold later for near your purchase price. There are many excellent choices out there that will sound better than 99% of the processors out there. Then you can upgrade later to the preamp you really need.