Will I see a big difference from my ifi zen blue to a denafrips ares 2

“Better” is a relative and very personal proposition in this hobby, so hard to say.  Read reviews and see if the Elacs may offer significant advantages over your speakers. You should share what improvements you’re looking for with a new DAC and what sound characteristics are most important to you.  With that information it would be easier to identify if the Ares ll might likely be an improvement or not. 

Are elac 2.o ub52 better speakers then my definitive technology studio monitors 350

I’ve heard both the iFi Zen Blue and the stripped down iFi Zen Air.

Both are excellent and will readily reveal mastering differences.

I was very impressed to hear some streamed Steely Dan recently. On this particular system I hadn’t heard such impressive front to back depth previously.

The best codec appears to be the LDAC.

My speakers  are definitive technology  studio monitor 350 and a speedwoofer 2  acurus 150 power amp  b&k reference 20 preamp.

@byner 

Yes of course you will hear a difference, but you might want to refine your question to include what other equipment you have in your system and what you are looking to hear.

I do not know about seeing but you may hear a difference cause one is chip DAC and other is R-2R. Two totally different topologies, you may prefer how one sounds in your system over the other. If you're serious about upgrading, consider Pontus II, as I hear Pontus holds the sweet spot in Denafrips lineup. 

Please explain  thanks 

Depends on your definition.