"09-19-15: Dylanfan
I read the Behringer has problems with overheating."
I never heard that. I've had one for 4-5 years and never had a problem with overheating. I know several people on Audiogon have one as well, and I don't recall any complaints of overheating. Its been out for a while. Maybe they updated the unit.
"What DAC in the 600.00 range do you recommend? "
Pick the one that sounds the best to you. lol. In all seriousness, though, your dac selection becomes much easier if you go this route. Like I said before, if you buy a dac or CD player to try and fix the highs in your system, you're basically buying an EQ with 1 setting, and you just have to hope it works. That's no way to fix a problem. As a general rule, using components for what they were originally designed for is the best way to ensure that you will be happy. I know some people love to through tubes and cables at problems, but that seldom works.
Here's a good example. If you currently had solid state gear, everyone would tell you to buy a tube preamp to fix the problem. That didn't work, so now they would say buy a tube amp. You already have a tube amp and preamp, but if you didn't, and went out and bought them, we would still be having this conversation because you still have the same problem. Now the recommendation is to buy a tube dac. Then they will tell you to buy cables, then roll tubes, then A/C products, then room tunes, then, then..... You'll eventually end up with the "then" that broke the audiophiles bank account, and walk away from the whole system in frustration.
The upside, is that if you fix the problem in your system the right way, picking a good sounding dac becomes much easier. You're not asking it to do something it wasn't designed to do. I already have gear that I've been happy with for a while, so I'm not current on all the different models currently offered. One that stands out for me, is the Parasound Z series. I like this one because you don't need special drivers. It works with Mac, PC and Linux. I'm sure that there are others like this as well. Some of the other posters will probably point them out.