which bang for the buck DAC?

Something to keep in mind about the PSA DL III is that it uses no op-amps in the output stage. Instead, PSA uses a 100% class A discrete FET output stage (most DACs in this same price range utilize an op-amp based output stage). Whether or not, this is why the DL III sounds so good, I don't know. It does sound good though, and the Cullen Stage IV modified version sounds even better.

California Labs Tube units.

I have the Benchmark and it works really well in my system (as a pre-amp with a Pass amp and Quad 2805), but I am not sure it will work well with the Krell if that sounds like the KAV300i that I had some years ago. The Benchmark is precise/lean and combining it with a Krell may be too much.

I've compared the Benchmark to the Apogee Mini-DAC head-to-head. The Benchmark was extraordinary, so detailed it was the musical equivalent of watching bodybuilders ripped for competition. Every muscle stood out. I thought, if anyone wanted to know what "analytical" sound meant, this would teach them. I was glad of a pause after a while, but I honestly wouldn't have missed the experience. You might love it.

The Mini-DAC didn't seem to leave out any detail but the focus was on the music as a whole, the relationship of parts within it, and with more sense of a performance event. I liked it better for a longer session. Furthermore, using the same transport and cable, the Mini-DAC's highs were less hashy.

So this is to recommend the Apogee Mini-DAC, at about $800 for a USB version on eBay.

Dacmagic - good dynamics, soundstage and extension. Top end a little too hot for my taste.
CI vda-2 - smoother, did everything ok. Transport was a Pioneer 59avi and there was not a whole lot of difference between the pioneer and the vda2 in direct comparison, couldn't justify keeping it. Keces dac was a bit better at less price.
MF a3.24 - best of the lot, a great buy at the used price it sells for.