Thanks for the pointer Maurice! I just went through HBs detailed review on that one. Sounds like steam is too slow for big milk drinks. At the most we do a breve on occasion so only a couple ounces of half-n-half. Still the steam performance issues of the thermoblock could be the explanation. I'm wondering if the thermoblock is fed from the boiler versus tank too?
No worries. I happened to know about the Silvano from my rather extensive searching when I moved up to my current HX. Up until then all my machines had been thermoblock/thermocoil Brevilles, with the exception of the ones I used during a barista course many years ago, which were Rancilios.
As for the steaming function of the thermoblocks, my experience is they were all rather anemic. To make up for the lack of pressure they pulse the pump. But there is a limit to this as any longer on cycle would result in water instead of steam (or the need for a much stronger thermoblock). Typically, they have only single hole steam tips and they take a long time to make decent foam. I got so I could make really nice foam even with my Cafe Romas. Going from that to steaming on the HX drove me nuts when I first got my Magister; a guy over on CG suggested I plug one of the holes until I got used to the huge amount of steam (which did the trick).
Concerning design of your proposed machine, it is certainly possible to use a thermoblock to boost temperature from typical brew boiler to steam. But I think none of the current machines do this. Some carpet cleaning machines have inbuilt thermoblock water heaters that boost the already hot (but not boiling) water to higher temperatures. But I wonder if this would yield enough pressure, unless a pulsed pump were used. However, this would require a non-standard (read expensive) pump, as todays most common vibe pumps could not stand the high temperature of the incoming water...you'd loose the diode and/or the coil due to the heat. Even running room temperature water the duty cycle is only 50/50 with a 1-minute max.
Concerning the brew temperature, with an HX or single boiler, I can surf the temperature curve and nearly instantly have the temperature I want. But with a PID and no HX I'd have to wait a while until the boiler water came to the desired temperature (unless the boiler were quite small and uninsulated). Not a big deal for some users I guess, but I like to mess with shots of different temperatures every time I start using a new roast...it'd drive me nuts.