For those that are looking for an excellent digital interface, try the SignaLink USB interface. The hookup is easy and the performance is excellent. The strong point is the built-in sound card that makes adjusting the correct transmit and receive levels very easy. I have had the major interfaces: RASCAL, RigBlaster Pro and one or two others. The RigBlaster pro requires many cables to hook up your computer, radio and any opitional speakers. I use the audio from my radio to monitor the band. The SignaLink USB uses twos cables: the usb from computer to interface and a cable to your radio. You have the option of using the radio's microphone plug--4-pin, 8-pin or RJ45 plug. These cables are purchased separately.
On the front of the interface(a small footprint) there are three knobs: one for transmit audio; one for receive audio and a delay. The instructions are fairly straight forward. The customer support is excellent.
The reports I get on psk31 are excellent. The interface helps me keep a nice lean and clean signal.
DX Engineering is selling the interface for $86.95 and the cables are $12.95. A worthwhile investment.
I purchase both of my interfaces from DX Engineering at the Dayton Hamvention. 73