The Synesso Hydra is 1 pump per group. I understand you can get just about any La Marzocco machine this way as well, but I've heard the lead times on that configuration are significant.

So is this different for other multi group machines? Or just the Pressure Profiled ones?

I'm not entirely sure what you're asking, but I will say that 1 pump/group is a very rare and relatively new thing in espresso machines. 1 pump per machine, regardless of the number of groups, is typical, indeed virtually ubiquitous. The Hydra was the first machine I heard of doing this, and it seems that La Marzocco has followed suit with the Strada and with adding the option to their other machines as BTO. I don't know of anyone else doing the same thing.

It's also not strictly required for pressure profiling. I believe the Slayer has only one pump, but uses needle valves and bypasses and the like to achieve pressure profiling on each independent group.

You appears that you have assumed the correct thing with my question! Thanks.

Now that I've successfully added pre-infusion to my single group/pump Linea, the next step is to design a mid pressure setup to complete my profiling project. In my mind, I want it all to be programmable and repeatable. But aside from awesome shots from Caffe Streets using the Hydra and Ipsento using Chad's awesome modified Linea, I haven't been impressed with machines that just have paddles that add pre-infusion only. I think to get the real advantage of pressure profiling, the machine needs a middle pressure and ramp up/down control.