Many posters seem concerned about the transmission of vibration from the speaker cabinet to the amplifier if the amp is placed on top of the speaker. IMO this concern is misplaced and over stated. The speakers are not flimsy. The Cornwalls are constructed of heavy plywood with a veneer layer. They are more than sturdy enough to support all but the most massive monoblocs. Tube guitar amplifiers are typically built to be positioned right on top of the speaker cabinet(s). The sound volumes from the guitar amps go much louder than home speakers, yet there is little regard given to vibration transmission. It doesn't appear to effect the sound, nor does it impact reliability. Are people forgetting that tubes are very rugged (that's why the Russians used them in their military jets). If you place the amps on an MDF board (or other material) and then isolate the board from the speaker with cork, sorbothane, etc. then you will have solved the "vibration issue". Is it as good of a solution as getting dedicated Gran Prix amp stands? No, but it's simpler and more cost effective than placing the amp in an airflow limited cabinet.
BTW, tube damper are a good idea whether you place the amp on top, inside, next to or even underneath the loudspeaker. They can do a good job at lessening thru air sound transmission artifacts.
BTW, tube damper are a good idea whether you place the amp on top, inside, next to or even underneath the loudspeaker. They can do a good job at lessening thru air sound transmission artifacts.