What should my next upgrade be? Your best experience

As a Vandersteen Quatro CT owner, I can tell you that they are amazing.  One of hte best values in high end audio I personally have owned.  That works in my room with my gear.  

What size room again?  What budget?  Speakers make  huge difference of course, but a top pre amp is important as is the source you feed it.  Cables to me are the last thing to think about.  ..What do you really want to change first?  Do you have a complete system in mind for hte end game?  That's important IMHO.  I buy a system rather than top rated gear and put it together.  Synergy is so important.  Heck, I've heard Vandy Treo's driven by an inexpensive NAD integrated sound better than a twice as expensive speaker from a top name maker sound worse when run with very expensive top rated electronics.  Just was a terrible match up.  JMHO

Teh nice thing about room treatment can mean a well placed quilt or two on the wall, a couple of large plants (real or fake) in between teh speakers or in the corners of the room.  Lot's of inexpensive and nice looking elements that will help the sound of the room.  Also a rug in front of the speakers if you don't have carpet is most probably a need too.  Just thoughts.

It all depends on what your budget is and what level you are able and want to play on.  Digital is highly sensitive to power issues.  It doesn't matter if it's a 500 Chord Mojo (I own one) that's battery run or my Ayre QX5 that has a power conditioner built into it and has built in optical isolation etc....  I have friends who own the Bricasti DAC/amp as well as the Davinci mk 2.....all of them need the proper filtering and power cord.  Digital still has inherent problems and that's why a decent TT combo will still sound more musical and more natural than any digital out there.  There are some areas where digital can be outstanding and with better clocking and design, they are getting jitter to where it needs to be so timing isn't off as much.  

There are outstanding value DACs as well as good sources, but you must try them all together.  Digital is so finicky.  You can't just say source A is great for the money and DAC A is also great for the money and assume they can sound good together.  Too many things will play into that like your rooms power, connections between the two, the way they both are engineered and which connections are max'd by each product.  Then you take into account your wifi if you stream that way (hard wired is always best), which ethernet cable are you using and what type of isolation are you using if any, both internally or externally.

Just too many variables in play here.  I personally buy systems.  That's what I'v always done and I usually don't buy that often.  I will make some changes if I feel they are worth the money and if I have the money at the time (just upgraded from Vandy Treo's to Quatro CT as I felt they were THAT much better for me).  

When I help someone put together a system, I usually take the budget and figure out the best source for them and then look at speakers they may like to get an idea and then fill in with the amplification.  Pre amps to me are SOOOO important.  

Garbage in = garbage out is true, but a great source can be ruined by a DAC, amplification, mods, accessories, cables and or speakers.  Same with anything else in the chain that is down stream.  That's why so many folks audition speakers and fill in from there.  I've heard better sound, personally, from GREAT speakers, good amplification and a decent source. Conversely, I've heard not so great sound from a wonderful source feeding world class amps run through average speakers.  Again, JMHO 

What is your budget?  That's the most important thing in recommendations.  I personally will have friends get the Codex DAC/headphone amp and have them run it directly to the amp unit they can afford a good preamp.  The Chord Hugo 2 is another good DAC, but costs more than the Codex which is 1800 list. The Marantz is about 2800 online.  You can get a nice streamer for 500 or so.  Digital is changing so much and that's why i personally go for separate units so you can upgrade as needed or as you want and not get clobbered as used digital usually goes down in value much quicker than anything.

I agree that the Marantz unit isn't up to the same speed as newer DACs'.

That said, do you even have music that is more than 24/192?  I highly doubt that you do or will during the life cycle of this product. It will do native DSD, which you may or may not have, but it doesn't list the specs.  I'm sure it's the lesser of the playback specs though.  

For the money of the Marantz, I personally feel that you can get much better quality, but it will be in a couple of boxes.  YMMV

Actually you ask if better build quality equates to better SQ.  Not always.  most of the products will be very well built in this price range.  As I said, it's still all about synergy with your system which folks dont' seem to want to discuss.  You have lot's of good price options from Marantz to PS Audio to Schitt to Mytek to Chord.  It will all depend on what will sound best together as a system.  Digital is just very tricky.