I have two blue hawaii se (golden reference hv and lv psus) , two joamat mini t2 (with golden reference hv and lv psus) and a diy t2. I only have experience with them using sr007 mk2 earspeakers. The hawaii is very good, far far far better than the stax srm006 or anything modern stax sells. The mini t2 is better still improving bass, micro dynamics and detail. The diy t2 is fantastic its takes the mini t2 strength and improves on it and adds better macro dynamics, even better bass and detail. If you can get any stax amp get the diy t2. As far as I can tell the sr007 needs as much drive as possible to get the best bass and dynamics and the diy t2 has the drive.... (we are still waiting for Kevin Gilmore to design a single ended stax amp which uses 300Bs or 211s or something even more powerful... 🙂 )
In terms of build difficulty the blue hawaii is probably the easiest (there are two version the original uses obsolete components but the modern version only uses transistors which are still available new), the mini t2 amp boards are almost all surface mount (psu is still through hole) and require precision and a good hot air station. For checking a stereo microscope is very useful. It only uses modern components and costs a bit more than the blue hawaii to build. The diy t2 is not difficult to build (if you use resistors that can handle the voltages) it's just big and intimidating. In terms of build costs the diy t2 is by far the highest. (there are two versions of the t2 one which uses almost all obsolete and very expensive nos components and a more modern version which only uses two types of obsolete transistors.). Either way you need to be aware there are many people selling fake nos transistors which will fail and blow up immediately on switch on or if you are "luckier" fail slowly over time. So you either need a trusted source or a transistor breakdown voltage tester and transistor identifier and even then you are taking a risk... (almost every seller of nos transistors on ebay sells fakes or a mixture of fakes and modern "equivalents" relabeled as originals.
In terms of size I built the entire blue hawaii in a single 400mm deep case, the mini t2, transformers in one case and the amp and psu in a single 400mm deep case. Diy t2 transformers and psu in one 400mm case and amp in another 400mm case. (I had to modify the diy t2 amp board gerber files for the amp circuit board to make it fit)...