Rebbi, I'm not Klaus, but I'm currently sitting in front of a Khartago amp. Note that in difference to the Stratos cases, the Khartago vents heat from the large holes drilled in the top cover; on the Stratos, the side panels are the heat sinks. I leave my amp on 24/7, and right now sitting at idle, it is warm to the touch but not hot at the vent holes. After playing for a few hours at a time (I have it hooked up also doing duty when I'm watching movies), it can get noticeably hotter at the vent holes, but not quite darn near burn yourself hot (like a Pass amp might?). If it were me, I wouldn't stack them directly one atop the other if you plan on driving them hard for hours at a time, but if you put some footers under the top one (between it and the bottom one's top case) to give you a couple inches worth of air space between them, I think you would be good to go.
Hope that helps, and I hope a few others actually running monos reply shortly. I do remember a conversation here on AC a few years back where I think someone was using a pair of Khartago monos in a desktop system where he had all his electronics stacked, and at some point decided to place the monos side by side, not because anything failed in the amps the way they were stacked prior, but simply being cautious about the potential for issue as you are asking about here.
