My question is where do you find the higher quality MAK everyone seems to mention?
One that is available and not trying to find a used one.
Well... Questar is available on demand, but not at 127mm, and not at prices most of us are going to endure.
This is probably the reason for the popularity of the Synta Maks: It's difficult to find other options, particularly in smaller apertures.
One simpler solution might be to go to a 150mm Synta Mak, the idea being that the extra aperture would help offset the mass-market-oriented optical shortcomings. Same could be said for a 6" SCT.
So what's the difference with the Explorer Scientific mak and a Skywatcher/ Orion maks?
f15 (ES) vs. f12 (Orion). Orion's are made by Synta, I'm not sure who does ES's manufacturing. Bresser supplies ES's scopes, but I'm not sure who makes Bresser; it's not Synta (or GSO.)
Generally, users have reported that the mechanics and finish, particularly the focus mechs, are better on Synta scopes than ES. Haven't heard optical complaints. I'm sure that optically, they're more similar than different (other than focal length). One might hope that the f15 was more forgiving of manufacturing tolerances.