I have a Jolida JD-100 and a Theta DSPro basic DAC. Theta's external DACs are very similar, if not better, than the internal DACs. So I feel this is nearly apples to apples.
They are both very good. Stock tubes in the Jolida would hand the competition to the Theta every time. However, upgrading the tubes, makes the race a lot closer.
I prefer the Jolida most of the time. The mids are sweet. I can change tubes for more air, or more attack, or even more bass. I like tube tweaking a lot.
The Theta has typical SS bass, which is nice. Also it has the typical aggresiveness associated with SS as well. This is sometimes good and sometimes not, it depends on the recording.
I wouldnt give either up at this stage. Both are good but different. The Miles transport mechanism is definately better than the Jolida's.