The next level of technical espresso geekdom I want to explore is variable times & pressures with pre-infusion. Are you going to tackle that with a SBDU? No, I'm not trying to argue, and I realize that is something no home/semi-commercial single head machine allows for right now .... just wondering if that's something on your Tex-dar...??
That seems to be the geek issue du jour, doesn't it? I'm not sure most folks even understand what it is and what its purpose is.
Preinfusion is having a way to let line pressure water soak the puck before the shot begins. Its purpose is to reduce channeling in the puck by wetting the grounds, letting the puck swell to fill the filter before the 9 bar pressure from the pumps hits it. It was a big thing back in the 90's when some commercial makers added it to their machines.
It seems to me the better way to protect the puck is via pressure ramping; using an air chamber to buffer the 9 bar pressure. Some folks have done this to Silvia's, but I've never seen the results presented as a graph showing the ramping effect.
BTW: My Bunn ES-1A has both features, and you can turn the preinfusion on or off as you wish.