To get the most from a dac what is required input?

I have a really nice Musical Fidelity Trivista 21 dac. To get the most out of this dac (not sure if it actually upsamples) I'm using a Krell KPS 20i/l as a transport and although it's a big improvement using the dac would I be better off with a different transport? To ask this a different way: What are the differences in the digital outputs of various transports and how do these differences affect the sound quality given a high quality dac? Thank you.
Jitter output is one variable in transports that can make a sonic difference. As to how much jitter the Krell puts out, who knows. Another transport, dedicated or not, could be better or worse.

Another variable is what digital out/in your transport/DAC is optimized for. For example my Proceed transport is optimized for AES/EBU output, my DAC optimized for I2S input, I should attain maximum sonic quality using a transport optimized for I2S with my DAC, or I could get a DAC optimized for IES/EBU.
Yes it upsamples to 192

I wouldn't angst about transports much unless you have a high resolution system that is highly optimized.

The easiest way to improve your transport is to move from a platter based unit to a hard drive transport. This will neutralize the jitter difference between transports by largely eliminating it.

And there are a whole bunch of other benefits which will lead to an increased appreciation of your CD collection and generally much more listening.