I have both an Advantium and a steam oven (Gaggenau combi-steam). I needed the oven capacity, as both can be used as straight convection ovens. OTOH, it depends on how much you cook and how you cook.

What I did not do was put three ovens in a stack. That's a bad idea just when it's a double oven with a microwave or warming drawer. Something is too high or too low, which leads to inconvenience, and, if too high, danger. With three different brands, you're going to need at least a couple of inches in between for cabinetry, because they aren't made to interlock or work with each other. If the Viking has plumbing that'll be a concern as well.

One tip I learned here, which was really excellent, was to have a special drawer just for the Advantium trays and rack. Mine has a couple of potholders and plate covers, too, but nothing that makes it hard to get at the trays and swap them out. People who just put the trays with their other tray storage, or in a bottom drawer, or in some hard to access place, report not using the Advantium to its full ability because it's too much bother.

So, I have the combi-steam above my Gaggenau single oven in one stack, and the Advantium over the accessory drawer over a warming drawer, in another stack. Both stacks have a deep drawer with interior rollout tray shelf underneath, which is very useful.

One thing I have found is that I'm not as happy with the speed oven mode results as I expected to be. It works, but it's not as good as slow. I need the oven capacity, but if I didn't, I would be fine with the Gaggenaus and a Costco microwave. The 240V Advantium, in oven mode, is a very good convection oven, unlike most microwave combos.