I can't give you a head to head comparison as I went with the upgrades right out of the factory after reading other user's reviews. What I can say is that the OPA627 op amps are highly regarded, and the upgrade price is very reasonable if you price the individual components. Maverick also does a burn in test on every unit before shipping, so you're out any DIY worries. It's not just a simple plug 'n play either - some assembly required as you're replacing the original dual channel op amp with TWO single channel amps (there's another one underneath the adapter board) ... twice.
That said, if it weren't for the reviews and head to head comparisons, I might have just gone with the stock setup. And always wondered what I missed.
Ditto on the tube. The baseline Chinese tube is rated adequate at best. Also subjective in that if you don't do any comparison, it probably sounds fine. I just went with the GE upgrade there also. Since then, I've developed a bit of a "rolling" problem here ...
Arguably, the most important part for fine tuning the sound to your particular tastes ... and I just couldn't stops myself ... I swear, I'm done buying tubes ... for now ... probably ... <G>
(Not shown is a 1959 Tesla 6CC42. Just added that to the collection. Considered the "holy grail" in the lineup, but ... eh. Sounds thin to me - I expect that's because it's OEM "new" and has real low hours on it - probably just needs some more burn in to make it sing.)
The tube of the day is a GE Command Series triple mica 5670. Surprisingly, that's my current favorite - surprising in that it's the cheapest one I got. Very defined soundstage and smooth all across the frequency range. Maybe a bit light at the deep bottom, and the gain is lower than the others, but hey, that's what they make sub synthesizers and volume controls for ...