More money toward better speakers or a better DAC?

after taking in all the helpful comments above, I remain perplexed but closer to a next step. 
I have b&w diamond speakers and a solid amp.  a dac will be helpful.  Bluesound node 2i dac confines the music.  
A new wrinkle above is learning the longevity of a dac can be short - 3 - 5 years? What causes a dac to deteriorate so quickly?
I believe it ain’t easy doing a great job converting digital to analogue.  
So many dacs out there and any choice requires a leap of faith.  I originally started out liking the chord tt2 and now believe this will be a great choice.  Absolutely amazed how many dacs are out there, a choice is soooo difficult.  
I liked the bartok, but it seems very overpriced.  The David seems excellent but tough to tame after purchase. I like the m scaler, which seems overpriced. And tt2 seems overpriced too.  But I want a good dac and it better last a long time.
All about feeling comfortable with a purchase.  There appears to be lots of good choices.  

People who say a DAC is for 3 - 5 years must be people who like to rotate gear. If you are into the music more than the gear a DAC can last you as long as you want. My $1580 DAC that I have now will last me until I die or it dies first. Music sounds great through it why would I change it?

I have a 20 year old SACD player, the Sony SCD-1. It is one of the best SACD players ever built. I had it modified about 15 years ago and then had to put it into storage due to lack of audio system for a few years. It is back in my new office system today and it sounds shockingly amazing. The DAC in it is not as resolving as the current DACs but the sound from that player is so addicting. It is not going anywhere. The 3 - 5 years thing does not apply to everyone.

That Chord TT2 would be a great choice. Could last you a lifetime. I am looking at the TT2 for my second mostly headphone system. Another DAC I am interested in for system #2 will be the soon to be released Luxman DACs. These should have the same conversion internals as the $16K SACD player, D-10x, but at a much lower cost. Likely in the TT2 price range.

It would have been helpful if you mentioned what DAC you were talking about. The Node2i  DAC isn't very good. The Chord TT2 is a good choice. The RME ADI-2 is a good DAC , Benchmark  DAC3 is another. you're right there are a lot of good DACs which would last you longer than 3 years. 

It is the Benchmark DAC3B in an all Benchmark system, DAC3B + HPA4 + 2 x AHB2 + Benchmark speaker cable + Benchmark StarQuad XLR (for all the Benchmark connections). My analog sources are connected by Audience AU24 SE XLR’s and RCA’s. I sold some more expensive cables to "downgrade" to the lower cost Benchmark cables.

I should add that system synergy plays a big role in my love of this system. In the past, I owned the DAC2 HGC and DAC3 HGC and it was not at the level of sound quality as the DAC3B with the other gear listed above.

If you are going to tell someone else they lack experience and are only capable of "reading" it is probably best not to follow that up by quoting someone else and using none of your own words to attempt to prove a point. Even worse, is quoting someone else, who themselves quotes someone else to prove their point ... but not really, they just provided a link to an article.

 

 

Charlie was a character, but unfortunately, the posts you link while having some wisdom, are also lacking.   The article linked to written by Barrie Gilbert at ADI does discuss slew rate limiting and other potential issues related to I-V implementations and virtual grounds using analog op-amps. However, that issue is typically more a concern with high speed, high bandwidth DACs, of which audio DACs rarely are these days with much of the analog inside. Of course, the simple fact that many op-amps for audio are specified in this condition, not to mention that a simple distortion measurement on the completed product will reveal if this is an issue in the completed design. When one links to an article, it is probably best if one understands it. I am not sure Charlie did. Discrete components are not a panacea either. Integrated devices allow semiconductor component matching not possible in discrete devices, much lower parasitic values, and often enable circuit complexity (in a good way) that discrete devices do not allow.   In Charlie's rant on China, and LKS, he just comes across to someone experienced as "angry". Absolutely there can be issues in assembly in China, but his "analysis" of LKS based on a flawed photo review does nothing for credibility. The pins on the DAC are not bent. Simply zooming in would show that the PCB pads have staggered solder mask foot print lengths which zoomed out makes the pins look bent. The black solder mask is obviously for looks. Picking on "Chinese" PCB mount heat sinks? That removes any sense of credibility from his writing.

 

Oh DAC versus speakers? Bluesound 2i is good, but just that. There are better cheaper units. Something just is wrong with the sound of it. Sounds like you have good speakers so an upgrade is likely worth it there, but realistically, for most audiophiles, and I would include the vast majority at almost any spend on their system, the speakers in combination with the room are the limiting factor. It is one of the primary reasons why audiophiles are always swapping out components. If you don't fix the basics, then you are never going to be happy with the sound. It will never sound right. The best analogy I can give is the difference between a professional photographer with a point and shoot camera, and a rank amateur with a top of the line DSLR. Sure, you zoom in, and those images on the DSLR will have lots of resolution, but the composition is awful, the lighting is poor, and the subject matter uninteresting. The images from the point and shoot won't have the resolution, and will have higher noise, but will be far more visually pleasing because the most important things w.r.t. what pleases people in an image will be far better. Everything does not matter equally in audio reproduction. I would rather listen to 320kbps MP3 on a really well acoustically implemented system versus 24/192 on an expensive but acoustically poor system. Sure I will recognize the limitation of the MP3 files, but overall it will be much better.