Agree on the Xformer Match. I often run it at 0.7 (defaults at 1.0). My new Dumble project has it at 0.5, the lowest I've ever run it.
I don't know about the EuroUber, but the Dumble has two gain controls. These make a HUGE difference in the openness of the amp. With the Dumble, I run the Input Drive at 2.0 and the Overdrive at 9.0. Also, I tried backing off the Input Trim, but left it at 1.0.
Okay, EuroUber only has the one gain control - I just checked. First place I'd look before going deeper is the Master Volume location relative to the Input Drive. I'd start with MV at 10 and work down. There is a happy spot with every amp, I've found. Turn Compression off, don't use a Compressor block, probably turn Depth off. I'm not sure what Master Volume Trim does - but I suspect it's a piece of the puzzle.
Finally, IME, IRs have a huge effect. I splurged $40 on the two new OwnHammer packages and have found them worth every dime. The hard part is there are so many great choices, but I tend to stick with Live/Vintage tones and go for cabs related to the amp when I can. However, my Dumble patch is running a Celestion G12-65 and Alnico Blue for IRs. These sound so good together - very alive and open - I will definitely try these on other patches. Lacking the OH IRs, I'd stick with the Fractal Mix series.