Question about Azur 640c Version 1 and a DAC

I own a Cambridge audio Azur 640c version 1. I am thinking of adding the Musical Fidelity Xdac, XPSU, along with my X-10 tube buffer. The MF and Azur 640C both were produced in 2004. My question is, using the 640C as a transport, will the MF trio give me that much more detail and better sound quallity? I use an NAD C370 integrated with Sonus speakers, REL sub, and cardas cross cabling. I plan on upgrading the integrated in the next year or so. SHould I upgrade the integrated first, and skip the DAC, or is the DAC a smart purchase?
From what I have been told, combining transports and dacs can be hit and miss. I think attaining a great synergy is a trial and error thing. I'm SURE people will disagree. I didn't want to go that route, so I picked up the Cambridge 840c. (24bit 384khz dacs). It has 2 sets of balanced inputs and balanced outs, also you can utilize it's converters by running to one of the two digi ins. Great unit, relatively inexpensive and has the detail you are looking for.
I know I didn't answer your question, but it may be something to consider.....good luck!
When I was looking for a transport, Spearit Sound told me to take a chance and try using the 640C as a transport. They said they absolutely thought it would smoke pricier units they could sell me. I was also curious if it's onboard dac was up to the quality of my Sonic Frontiers Assemblage 2.7 Platinum dac. Well, the onboard dac of the Cambridge was not remotely in the same league as the Assemblage. But it does make a great transport. You can't be sure about synergy with the Musical Fidelity, there's always an element of serendipity about these things. As to whether you should upgrade the NAD first or the digital front end is hard to say. It's a chicken and egg kind of thing. A good used dac is going to likely be cheaper than upgraded amplification though, that's for sure.