Easy to discriminate between DAC ??

do not have the possibility in making A/B tests so i need to plug-deplug every time.
So far tested 4 different DAc but not so easy to find the better.
The sound timbre is really very similar, what I found different is the following:
- The slightly darker/warmer is Theta Chroma
- The slightly more transparent is CEC DAC integrated in TL 51Z MKII
- The slightly more nuance devoted is Swissonic DA96
- The clearly more aggressive is Minprint DI-Port
So what??
Can it be that the oldest one of the group,Theta old fashion 16 bit still sound very modern ?
How to make a jump in quality ?
Or it will always been a question of the personal taste of sound to make the choice ??

I would love to exchange opinions about and sorry for the elaborated question
Your question is a good one. I am surprised every time I listen and try to discriminate between DAC's. I found it so difficult to articulate any differences I (thought) I was hearing between different DAC's that I sold all I had and went back to one-box players. I have an old CAL Icon Mk II with an 18-bit DAC inside that sounds absolutely great. I have tried running a separate DAC with it, but really could tell no difference, certainly no improvement, so I'm back to the one-box model for now. My other player is a Marantz SA-1 and I do not use a DAC with this SACD player. I have owned Meridian DAC's in the past but had to go really far up their line to finally improve on the sound of a one-box player, to me. So yes, I think you can get great sound and satisfaction with old technology DAC's. But people rave about the latest upsampling DAC's too. It is always a question of personal preference, and what you can live with for the long term. Most A/B tests require spot decisions. Ideally, you should listen to a component for months before deciding. I don't think I've ever taken the time to do that, but I've certainly discovered how much I like or dislike something I've purchased after months of listening.
Sc53 last sentence is right on target! I might add my opinion for digital listening... real live musical instruments and voices do not have edges around them. The other unrealistic digital artifacts I have noticed are an unnaturally forward soundstage and unusually fast and aggressive transients (such as snare drum hits that sound like gunshots). I also try to listen to analog versus digitally mastered CDs, there should be a clear difference.
I think ABing can get confusing sometimes, and I don't think I can get a good feel for something without living with it for a few months. When I first replaced my Bel Canto DAC 1.1 with a Kora Hermes, a big difference didn't register with me immediately. But after listening to it for over two months I realized that there were very noticable differences.
The differences between DACs should be pretty clear.
How do you have the DACs isolated (placement/cones/stands)?
Remember, all DACs contain a preamp to get the signal to 2.0 mv, so place away from other electronics (if possible) and experiment w/isolation tweaks.
What is the rest of your system/cables/isloation stands?
Benthar I can't really isolate it more than the 1 mt cables.
The comparison is made with same cables apart when I compare the dac vs the integrated CD player (CEC) because in such a case I have one additoonal step made with a cheap SPDIF that is probably to my perceive a analog cable 75 ohm not the best for digital signal.
But i can't believe that changing it with a proper cale all the DAC's will improve dramaticaly vs the integrated Cd player. what's the rational here ?
You know i wanted to buy expensive SPDIF cable only when decided for the right one. This because some of them accept AES /EBu and the integrated CD that i could use a transport only will have a preferred digital out in AES. That will be the cable, but sometime dac like theta chroma get only the spdif, the one cheap I have today.
Tks for further comments and i will try to pute cones below. Would you go for rigif decoupling or soft decoupling ? you said cones so I guess go for rigid

At the end all of them have been tested without decoupling .
I have been able to hear very noticeable differences in DAC's. As to which DAC works best in your system, that will vary with the rest of your components, your personal preference and the digital cable that you are using. You might find that you like / dislike specific attributes of a DAC and changing the digital cable may change all of that. At least, that has been my experience. Sean
Differences are there but are usually small. It's really one of those things where you miss what it did for you only after it is gone. Even via remote control with quick a-b versus a good internal dac may just yield small changes, but in time the small things add up. Are DACs overpriced for what they offer? Of course, but most become immune to the reaming in the hobby in time, and many get excited over thinking they just might be hearing a minute difference and instantly deam it as a huge improvement, touting it as the holy grail over the internet to affirm their obscene spendings, but such is the audiophile psyche....