I can only speak of experience with their UN100D mini PC which I use as a home server in a fairly constrained closet. Not a hot machine by any means, far from that, but the cooling seems pretty decent even for this low power CPU.

BD790i that I just received (didn't even install anywhere) has a rather substantial heatsink over the CPU similar to high wattage GPUs. The chip itself is rated at 55W TDP so it shouldn't be that much of a problem cooling it. The motherboard doesn't come with a fan and I'm definitely not going to spend extra on high-end ones at least just yet.

I don't know anything about the thermals of 790S7's case though. It looks like they gave it at least some thought judging by the duct over the CPU, but how it actually performs I have no idea.