DAC needs a Pre Amp ?

If I understand correctly, your computer/dac has too much gain and you can't control the volume. I haven't used a mac in a while but I think you can go into preferences and change the sensitive the volume control. Kind of like setting the mouse up to move faster or slower when you move it. If you don't have adjustments to work with you may have to go with a preamp. I don't know what your budget is but to me, the preamp is very important to get right, and that usually means spending a lot of money because it is very hard to get something that sounds good at a low cost. So, basically, my opinion is if you can't get a really good preamp then don't get one at all. I would go with a passive unit because you don't have to spend a lot of money to get something that sounds very good and you avoid all the problems that a cheap line stage brings with it.

Unsure if you have an external DAC now? Many DACs now have volume controls and can double as preamps. From the inexpensive Emotiva to the popular Cambridge, and on to the well regarded Wyred 4 Sound.

I have an external DAC. Ayre QB-9 most all music software has volume control through the computer. Songbird, iTunes, Pure Vinyl, etc. they all have a slider to raise or lower volume. What I'm asking is. Would I get better results letting the DAC play at full volume and control with a preamp or does it make a difference?

I've only recently experimented with bypassing my preamp and going directly from DAC to power amp - the results are amazing - you're already there. I'd agree with Jkj25, if you can't get a great preamp don't get one.

So then is this the question: Does the volume function of my computer's "Player" software degrade or change the quality of the digital signal going to my DAC?

It's an interesting question and probably similar to whether DACs with "digital" volume degrade the signal when set at less than full. But again I think Jkj25's suggustions are good, passive if you must, I'd be inclined to stick with with your software for the time being.