Depends on exactly what you are after. I just mentioned the dx5 specifically because it is an all-in-one that does everything great and has some almost top chart measurements.
If you wanted to go big on topping you could go with an A90 and a d90. Or you could go all the way down to the bottom of the stack and get the new l30 and e30.
Personally though these cheap products tend to have cheaper pots which have Channel imbalance at lower volumes. Also longevity is in question with any budget product. Whereas something like the dx5 has all of the features in one along with a nice OLED screen and a clean aesthetic. Has enough power for most headphones and all the features that you could want for listening to any kind of music you desire.
If you want to go the really expensive route then you could drop 1200 plus dollars on an RME ADI 2. You get some Hardware equalizer and a fancy color screen, but the objective performance is lower than that of the topping.
Sabaj (which is affiliated with SMSL) also has a few recent models that are quite good and they are all in ones with pretty decent Aesthetics too. The performance is also up there close to the dx5 and the prices are pretty affordable. You can find the reviews on the front page still because they were just recently reviewed.
Personally I like topping over smsl after having owned both brands.
Outside of the list of recommendations here you are more than welcome to go click on a review and then when you reach the Giant image of top ranking products you can download that image and flip it sideways in order to find more products to look at in the top range of performers. There are two separate Graphics one for amps and one for DACs.
It is best to get these images from the most recent reviews as they are updated per review.
If you have some trouble with doing this I can also link the images here when I am near my desktop computer.
Thank you very, very much for your summary - this helps a lot.
My primary focus is on sound quality and logevity. I don't need balanced connectors and while a display would be nice, I can't really live without it. I only need an audio out jack and a volume knob in the front. In the back I need a coaxial and USB connector, that's it. I also don't need any mobility, because I will only listen at my desktop.
I would like to stay pricewise under the A90+D90 combination. A few question on this:
1) What quality difference can I expect between the DX5 and the A90+D90?
2) What solution would you suggest in-between (considering price) the DX5 and A90+D90?