While not vinyl but cassette I have used the direct input on my on board sound card to record over 300 90 minute cassettes just connecting direct from my tape player to the input on the card. I have experienced no loss of quality at all and I would recommend this route as the way to go.
As a former DJ of 30 years experience I also have tons of Vinyl that I eventually want to put down on the PC, I have tried USB turntables in my local store on high end rigs and the quality was not good, most likely down to the cartridge and needle an awful lot of noise from them.
I see you are using a Bang & Olufsen turntable and have I assume quality needles for it, I would just plug it directly into your PC and see how you go from there. As for software I would go with what the other guys have said.