stacking DAC on Monster power conditioner

It goes without saying that the best option is to avoid stacking when/if possible. If you must stack, the component which does not require passive cooling through vents in its top cover would be the one to place on the bottom. It's component suicide to place a component that does require passive cooling via it's top vents beneath another component, where the separation is only a few inches. Also, the footing plays a role. A piece of gear much larger than another piece usually means the larger piece need to go on the bottom.  From a sound quality perspective, it would probably be best to isolate your DAC, although you may be hard pressed to hear any negative effect. So in answer to your question, its not necessarily "bad", just less than ideal. 

@ thank you for the affirmation... The Brooklyn has vents on the top and bottom....I'll look into some kind of isolation feet for a little more air.... 

I stack. I add in some spacers.
Generally most equipment which generates only modest heat is no problem. My DAC has  only 1/2 inch above it, no problem left on 24.7
Some items, like a tube preamp, can generate more heat, and may need a little extra space.
One way to allow space is stagger front to back. So the lower item has plenty of free space to the rear and up... The heated air leaving the back itself will suck the heat out of the space between
I also use a shield between two components. Extra rubber feet then the shield, then the upper component. So the heat from the bottom one is not added to the top one.
For most items I use 1" tall rubber butyl bottle stoppers added in.
And I leave almost everything on 24/7
I have ten components in 4 shelves. Stacked 2/3/2/3
Nothing gets warmer than if it was alone.