External DAC for Cambridge CXN (V2) and Sony XA 5400 ES

I had the Benchmark DAC 3 in my system for a few weeks on loan (running into a Mastersound tube amp). I have  CXN transport and CXN V2, and when running either into the DAC3 I found that although the DAC3 offered a very slight increase in detail, the stage was very 2D and somewhat boring. Probably technically more linear, but just not engaging to me in my 2 channel system. I really enjoyed the Benchmark with my headphone rig, but it just didn't do it for me in the main system. 

Another option you may want to look into is the Modwright upgrade for the CXN. Very few real world reviews so far, but it looks very interesting in my opinion. 

Maybe a local dealer (if there are any left) would have one that could be tried.

I would also love to try the Bryston, but dealers are one of their biggest challenges. I think it might be easier to find someone who owns one nearby to host then to find a dealer honestly, depending on where you live of course. 

On the Modwright, I totally get that. It requires quite a leap of faith. The only reason I'm considering (if I can get the funds together next year) would be because several people who's ears I trust have spoken highly of Modwright gear, and the design seems to be aligned with other gear that's stood out to me. 
I'm a sucker for Class A designs. Both my main amp (tube amp) and my headphone amp are class A. Those designs always seem to connect with me. Secondly, this mod makes the unit a dual power supply DAC. I've noticed DACs that leverage a dual linear power supply generally stand out to me as well, tube or solid state. Not that I'm a DAC expert, but that's a trend I've noticed. 
Then you factor in the fact that I almost exclusively use the CXN for streaming Tidal, Spotify and playing CDs. I personally don't have an SACD need, or even an ultra high res file type for now.  Plus Cambridge is on the early list Tidal Connect, which will make Tidal streaming even easier. 
Lastly, there's the price. I think this is where Modwright kept it really competitive. His gear in general tends to hold value very well. I've already had the CXN for awhile, and those are holding value fairly well too. I figured if I got it and didn't like the change I could sell the CXN and mostly just loose out on the shipping and normal CXN depreciation. At the same price point and general functionality is the Lumin D2 and Auralic Altair G1. I think there is good arguments for all 3 units based on needs/priorities, but if I was going to one of those units I think I'd rather go separates with the streamer and DAC. Because I already have the cxn, the barrier of entry is lower with the Modwright mod.  

In your shoes though, getting something that can take DSD directly from HDMI sounds like a key feature, and I think that's a good consideration. Looking forward to seeing which way you go and your thoughts wherever you land.  

First shootout will be the Benchmark fed by the Cambridge digitally to my AR preamp via balanced interconnects against the Cambridge on it's analogue cables to my pre.

I'll be interested to hear your findings as I've done a similar test but using RCA on both. 
Don't forget to level match. XLR/balanced outputs normally have a higher output voltage, giving it a general advantage. 
If you can test both with RCA or both with XLR you'll have a more apples to apples comparison.