The short answer:
I've never installed any of these kits on a Giotto Premium. But I have tinkered with my own direct plumb setup and can offer some insight. With that caveat, what follows is the long answer
Chris' Coffee sells two direct connection kits and one float kit. The two direct connection kits work essentially the same: A normally closed solenoid piggybacks on the pump terminal connectors. When the pump activates, the solenoid opens. Each kit includes a pressure regulator. Technically vibratory pumps are designed to operate with no inlet pressure, but apparently they tolerate modest pressure without long-term issues.
The float kit works like your typical toilet tank, i.e., a small float controls a valve and keeps the reservoir filled:
Image courtesy of Chris' Coffee Service (Float System)
My espresso machine wasn't direct plumbed using either of Chris' kits since it came from 1st-line, but the hookup is the same: Main water inlet -> filter system (optional) -> pressure regulator -> solenoid -> pump -> espresso machine. The rest are details about the fittings and connections. Back to your original question, will either of these kits work with your Giotto Premium? My answer is a qualified "yes". I qualify it because they are not "plug and play" solutions specifically designed for your machine. I've installed the direct connect kit for the Andreja Premium as part of its Buyer's Guide
Image courtesy of Chris' Coffee Service (Andreja Premium Direct Connect Kit)
The parts are straight from the factory and instructions are detailed and easy to follow. Chris' other direct connect kit is shown below:
Image courtesy of Chris' Coffee Service (Direct Connect System)
I've not installed one of these, but the same parts are there (solenoid, pressure regulator, fittings), simply adapted and documented for a specific group of machines. This isn't rocket science, but as you found talking to their technicians, they can't assure the kit works for your machine. I believe a competent do-it-yourself'er could adapt either of the two direct connect kits to just about any vibratory pump espresso machine. The float system depends on clearances that can make it tricky, as Dave documented in Quit Filling That Water Tank
, but it would probably work well too.
Speaking hypothetically, if I were to buy one of the direct connection kits to apply to vibe espresso machine X, which would I choose? The kit designed for the Andreja Premium is a little more expensive, but includes braided stainless steel wrapped tubing, a better pressure regulator, pressure gauge, and a smart design that is nearly universal - the usual "main inlet -> pressure regulator -> solenoid" sequence ends with a barbed fitting that accepts the standard silicone tubing used as inlet hoses for every reservoir machine I've seen. You set the output pressure so low (0.5 ~bar, IIRC) that you can simply slip the pump's tank hose right onto the direct plumb barb fitting. When I was evaluating the Andreja Premium, I used the direct connect kit and switched it back and forth several times between direct and tank in less than a minute (the back shell of the Andreja has enough clearance to accommodate the fittings and solenoid while allowing enough room for the tank).
I'm not saying that any
of these kits will work straight out of the box. I'm not saying what modifications, if any, would be necessary. I'm not saying that it would work specifically with your Giotto Premium. I am certain that Chris' Coffee will say the same thing - except more emphatically - and will add reminders that they do not give refunds on parts and will not offer free assistance. However, it's my educated guess that the Andreja Direct Connect kit could
be adapted by a competent do it yourself'er with little difficulty. The Isomac Direct Connect kit could also be adapted too, but I think it would be slightly more difficult because it lacks the nifty barb fitting and pressure gauge included with the other kit.
DISCLAIMER: THIS POST IS FOR INFORMATIONAL PURPOSES ONLY. I WILL BEAR NO RESPONSIBILITY FOR ANY PLUMBING FAILURES, INJURIES, OR LOSSES RESULTING FROM ANY ATTEMPT TO PERFORM ANY MODIFICATION YOU UNDERTAKE. PLEASE REMEMBER THAT ALL PLUMBING INSTALLATIONS MUST BE INSPECTED FOR CONFORMANCE WITH YOUR LOCAL CITY BUILDING CODES AS REQUIRED BY YOUR LOCAL ORDINANCE, HOME INSURER, ETC. MODIFYING YOUR ESPRESSO MACHINE WILL ALMOST CERTAINLY VOID ITS WARRANTY.