Computer based system. Need advice on DAC.

Get a dac with a volume control. It will allow you to get rid of that old preamp. Removing the preamp will probably make a bigger difference than the dac itself.

"In generally, I now lean away from spending a lot on a DAC. Differences in upgrades are often quite incremental, and technology is changing daily -- meaning you'll likely want to try new things, and there a good bit of high quality "yesterday's gear" on the used market."

Can you give me some examples of what you are talking about here? Things always change, but on a daily basis? I never got that one.

"The recent introduction of DSD is one such example. If one bought a megabuck DAC w/o DSD, and then really liked DSD, one might be a little distressed."

I guess it all comes down to what you consider recent. DSD came out about 16 years ago (I think 1999).

"06-30-15: Schubert
Thestyx, have any idea if the UD-301 can handle Symphonic Crescendos ? To my ear a lot of DACS can't ."

The analog section of the dac is mostly responsible for that.

"News to me! Live and learn, I guess. Zd542, could you name some of the 1999 DSD units that were in commercial production? Would you consider any of the the 1999 units an option for the OP?"

It depends. For me, the only way I get involved with DSD is with SACD's. As you know, there are any number of players that support the format. Theoretically, you could have bought an Elgar DAC in 1999 or 2000, have it upgraded periodically, and its still considered one of the best in the world today. And, yes its not a cheap DAC. But the real question, is do you really need DSD and is it worth getting involved with outside of SACD's? I say no. For hi res using a computer as a transport, I don't think it sounds any better than PCM. Also remember, Sony pulled the plug on DSD about 10 years ago and is considered by many to be a failed format. I think if the OP stays with PCM formats, he can use the same DAC for quite a while.

Another thing worth mentioning is if you judge a DAC based on its digital characteristics, you're only judging half the DAC. The analog portion of the DAC has a huge effect on its sound quality. If you don't consider the analog section, you're really missing out on a lot. In most cases, what separates an exceptional sounding DAC vs just an OK sounding DAC, is the analog section. And I think it goes without saying that a better overall sounding DAC will be kept longer by its owner, regardless of specs or formats.