Hi Ian
Got a lot of variables to work with there!
Learning any new machine setup will require some tweaking, but from what you've said I think the major variable here is possibly going from home roasted (lots of possible variation here) to commercial beans (less so - especially from one supplier). If you're firing up the corretto again soon, maybe fiddling too much will be counter productive - you'll need to do it all again when you change back. But if you're going to stick with Andy's beans…
It is possible that the new machine is running cooler than the Silvia, and the fluid/pump dynamics are a little different too. If you're used to lots of thick, dark crema, this may be part of the cause.
I'm not a big one for endlessly discussing different basket sizes etc. If I were in your situation with those beans though, I would consider that they are possibly roasted a little faster and lighter than you are used to from your home roast. I would tend to fine up the grind/dose higher/tamp lighter and see what result you get. I normally use 19.5g in a standard Diadema double basket FWIW. If I get thin pours, this is what I tend to do
Cheers Matt