Should I mod my original MHDTParadisea or uprade

I'd wait till the version 3 arrives and then decide.

How/where would you have it modded? For the money, the quality and part count is high on their products. Personally I preferred the DIY Paradise USB Monica. If I were you I'd be collecting different tubes for it to try. The tube (forget which) is not intended to be used as a high fidelity audio tube. I went through many tubes (I am lucky as a close friend is a tube dealer). Surprisingly, the tubes he thought would be the best (WE, RCA) weren't. The one I did like was a re-branded give away. If my memory serves me correctly, most of the tubes had euphonic microponics. Some tizzy, some with dark bloated bass ect... FWIW, at least 8-10 tubes were tried, even multiples of the same vintage NOS WE. All were different, most bad.

Hmmmm, I assume 4est that you are talking about tube rolling in the Paradisea(?). I'm not familiar with the Monica but I do have a Paradisea and have done some rolling there myself. I can definitely agree that the tube will make a difference, but I did not have the same experience with so many negative attributes in the tubes I tried out, which were only 4 different tubes. I'd have to look up notes, or a previous post to recall my specific impressions, but recall that the three NOS tubes I tried certainly sounded better than the NOS tube they supplied with the DAC. I believe my order of preference was widely difficult to come up with, but went something like - Bendix 6385, GE 5-star, WE 396. I don't recall any of the three dishing up any notable stridencies as 4est observed, but (s)he tried more than twice as many varieties as I have. I'm using the USB version btw. Damn fine DAC for the money. My friend currently has both the Paradisea USB and their new Havana and says the Havana is marginally better - I did not get any details as to why. Probably can find some input online on that subject.