Discussion of various types and blends of commercially available pre-roasted beans, their best sources, prices, their respective merits, and the Vivaldi settings required to optimism flavor.
94 seems to be a happy setting for most people on the VII, you can certainly jump to 95 and 96 to see where the breaking point is on that particular blend but I think that's where you'll start tasting the bitters.
Was it flat on the 93C setting?
Try it at 95, if it handles OK...try it at 96 but back off a little. What I mean by that is let the group cool for about 20 seconds after bringing it up for a warming flush. You need to play with the heat that way so you can get the exact temp you want.