Volume control w/PC keyboard is possible if you go the conventional route and just use your onboard soundcard as well as its analog out. However, since it appears that there is some dissatisfaction with things as they are, generally it is considered a good idea as you suggest to use an outboard DAC. Under this configuration the DAC receives an S/PDIF signal from your computer's digital out. The signal can be electrical (coax) or optical (toslink) - depending on the audio interface used. In addition to the devices listed above, another popular choice is the M-Audio Sonica. These will do if all that is desired is use of the computer as an output device. In all these cases, conceptually, the computer just functions as just another digital source, so volume control is performed by your preamp, integrated amp, etc - whichever device which does attenuation duty.
If however recording capabilities are also desired, then further layers of complexity are introduced. In this it may be useful to search the web for "daw" (digital audio workstation) related websites. (Audiogon is not strong on computers and audio.)
For the purpose stated -- just radio -- the expense incurred for an unwieldy and esoteric setup may not justify the ends. Perhaps the shortest (and least expensive) path is simply to upgrade the soundcard in the computer. If that is not possible (say, a notebook is being used), then a USB device, such as the ones named (for example) will likely be needed. I hope this -- limited -- reply helps.
If however recording capabilities are also desired, then further layers of complexity are introduced. In this it may be useful to search the web for "daw" (digital audio workstation) related websites. (Audiogon is not strong on computers and audio.)
For the purpose stated -- just radio -- the expense incurred for an unwieldy and esoteric setup may not justify the ends. Perhaps the shortest (and least expensive) path is simply to upgrade the soundcard in the computer. If that is not possible (say, a notebook is being used), then a USB device, such as the ones named (for example) will likely be needed. I hope this -- limited -- reply helps.