Stacking gear no more rack space does it affect sound quality

For anyone who is concerned about EMI/RF noise radiating from a component and affecting another one, you should realize how EMI/RF radiates. Unless the component generating the noise is fully sealed, EMI/RF will 'escape'. A good product design will take into account the generated noise and will deal with it as part of the design, not as an afterthought. Half measures, DIY approaches, etc  simply don't work with radiated noise .

And heat does not necessarily kill components as long as you keep the minimum required clearance and / or ventilation around the component. Of course you should not block ventilation slots. There are many components designed to operated at very high temperatures. 

greg_f - Have you ever done failure analysis? I was a Failure Analysis Engr. and worked in screen rooms... Duh!

@fiesta I have calculated MTBF as part of the design cycle in several products admittedly nothing to do with hifi. Your point is? Are you telling me that a device operating well within its specified limits will fail prematurely? Sure its performance may degrade if operating continuously at its limits but the design of the product should ensure that all devices are operating well within their operating limits, else it is bad engineering practice.

Well at least you know what MTBF is. Does that mean if you operate something below its designed temperature span, it will NOT last longer? I have seen a lot of poor engineering in my day, one common one is REL's R8 failure in several of their subwoofers. Another is using polarized 35 vdc capacitors in a circuit that exposes them to 25vac rms repeatedly. They never made it close to operate to their designed MTBF. Many manufactures including ones that designed equipment for military use, have poor designs, yet somehow they get qualified! I'm pretty sure in todays hi-fi audio world, manufactures use inferior designs and components specifically so they will fail and must be replaced, just to generate more revenue. There are so many examples of this in products from the automotive and appliance industries. Shall I go on? If you operated a piece of electronics in a narrower temperature band than its designed operating temperature specification, it WILL last longer!