Maybe I should admit defeat and get a Signalink ?
The SignaLink has three things that make it handy:
1. A USB-connected sound card _with a knob_ to set the TX audio level.
2. A "digital VOX" circuit that keys the transmitter, so you don't need a serial port to do TX/RX switching. When it detects audio from the computer, it switches the rig into TX mode.
3. A "breakout box" to connect the SignaLink's internal wires to the rig's interface cable.
IMHO, it is over-priced for what it does.
But people who buy them have less trouble getting their first contact, than people who buy anything else.
With a SignaLink, if your digital-mode software is set to use the SignaLink's sound card (which shows up as a "USB Codec" under Windows), and your rig is set up right (use the "packet" settings in the manual), you'll be able to work digital modes.
You'll have to decide how much frustration you'll suffer, to save $100.<g>
PS -- the first digital contact is, by far, the hardest one you'll ever make. Once the hardware and software is set up correctly, it's all "point-and-click".
PPS -- I'm using a 10-year-old BuxComm Rascal interface at home -- just a few parts in a plastic case. But for my club's new Field Day station, I got a SignaLink. The following year, the station was "improved" with one of the RigBlaster interfaces, which would handle hard-keyed CW. It took three of us, testing for a few hours, to figure out that the RigBlaster was faulty! So don't think that you're alone in having startup pains.