Who has upgraded their Cambridge AZUR 840C CDP to the new AZUR 851C CDP?

I really like my Cambridge AZURE 840C and am wondering what I may be missing compared to their new offering, the 851C? I use my 840C 80% of the time as a DAC, streaming TIDAL and have it connected to my Wadia 171i IPod dock. I have not had a chance to hear their new CDP, and found conflicting reviews on-line about it. Some of the negatives were a noisy transport and some frustration when selecting between three output filter options. On the good side I have only heard that "it sounds better", not a very in-depth description! So, please, if anyone out there has upgraded to the new 851C offering from the 840C, I would be very interested on your thoughts and if given the chance, would you do it again? Another thought was to just upgrade to a better DAC and use my 840C as a transport, but I would have no idea where to start with this potential upgrade path and keep within budget.
Never owned the 840C, but have compared the two side by side on my dads system. They’re definitely different from each other and I can see how some may prefer the older unit. To start with the casework on 851C is hands down a better box. Some feel the 840C is warmer and I think at first it does sound that way but the truth is the 851C is so much more revealing, has more air and more extended on top and bottom.

When we listened to the 840C it sounded very similar to my dads CA DAC Magic. The 840C might have been a smidge better but it wasn’t by much. Still a nice player.

I love my 851C and I will tell you it really shines with great cables. At first I used Clear Day Cables Balanced IC with a Kimber PK10 Gold PC and that worked well, but switching over to WyWires Silver Juice II PC and Silver Balanced IC has taken it to another level. I also switched out the two fuses to SR Blacks which really opened things up.

In my opinion the 851C is hands down the better machine, but if you do not have or will spend the money for nice cables you may not hear much of a difference. The 840C is still a very nice machine.
Thank you, adg, I appreciate your response!

I am currently using Kimber Balanced Silver Streaks feeding my Krell Amp from my 840C. You mentioned good cables required to realize the SQ improvement, do you think the SS are in that category? My Power Cable is WireWorld by Nordost. In my system the Krell is very resolving/unforgiving and a bit aggressive, and maybe that would be a concerning factor moving to the 851C. What are your thoughts about this?

Thanks, again!
Kimber SS is a very good cable; used a KCAG a lot which I like very much. In comparison my Clear Day Cables balance is very similar to the KCAG. The WyWires Silver has all the extension of the other cables we're talking about here but by comparison the others seem stressed where the WyWires has a very relaxed open stage but still a fast cable. 

I've dragged home a few Krell's and although not my preference I had no problem with them either. My CA 851C sounded just fine on them. The 851C by no means is bright or edgy but it is neutral. I play a lot of vinyl and I feel my 851C gives my vinyl set up a run for the money. It's really a nice player.

Guessing on your PC's you meant WireWorld and Nordost; not familiar with WireWorld by Notdost. I have not heard the top tier Notdost which I'm sure are very good if not great for all the press they get but the more affordable offerings I've heard I found could be a little lean. Always like WireWorld and even their more affordable cables sound very nice. We have a local Nordost and Kimber dealership but lost WireWorld awhile back... too bad.

If you like your 840C I'd keep it. If you want a little more air try some Synergistics Research Black fuses. You'll be amazed how much it will open up your player. All the resellers have a 30 day money back guarantee on them but give them a good couple weeks for them to settle in. My 851C has two fuses and I suspect your 840C is similar. One right by the transport and the other was hidden right under where the IEC socket is under a little black piece of plastic - it's hidden. On the 851C I had to pull the side panel off to get to it.

As far as your Krell goes I would look for another IC cable. Kimber SS isn't something I'd use on a Krell, or Clear Day Cable either which I own a lot of and really like them. WireWorld would be something I'd look at or WyWires Silver which is not a silver conductor but just the model name. Plenty of great cables out there, so I'd experiment with cables before I ditched the 840C because it's still a very nice player.

Look into the fuses first. Will cost around $250 for the two fuses which seems stupid for a couple fuses but they work.
Thank you very much for your response! I'm guessing the CA 851C is better but not necessarily by an order of magnitude, and that alternative IC's and fuses would be the more practical choice at this time. I will eventually upgrade my CDP/DAC at some point in the future. I read reviews about the 840C and many said that it made for a great transport, so maybe my focus should be just a new DAC as I mentioned about >80% of my listening is using the 840C as a DAC.
Hi grm;
About 2 years ago I upgraded from my 840C to the 851C. Certainly no looking back. I was not unhappy with my 840C until I heard them side by side. It only took 3 cuts on a  reference CD and 4 switches back and forth ( not an immediate a-b comparison) by removing the cd and hitting play that the decision was made. Big difference to my ears. As above described by adg plus to my mind more engaging musically. Don't really know how else to describe it. It also beats the hell out of my compatriots unit purchased shortly after my 851C came home. When Brian asked me what I thought of his new CD player (he had given it to me while on holidays as I was curious how much better a unit that cost a little over twice as much as the 851C would be)suffice to say my words were couched but the friendship is still strong. and he thinks it sound very good. Take this as you may at this late date of reply. Cheerio, dmg
I bought lately the Cambridge Audio CXC cd transport which is actually the same unit as the 851C but without the inner dac and pre sections it is connected to my Macintosh pre/dac and the sound is really amazing, I think it’s better for you to buy the CXC and a standalone proper dac and to connect them with a good coax cable, I assume this will give you the best sound.