That is a very interesting experience about the Airport Express... good to know.
I checked a few of my LPS's with a Trifield 100XE meter, and the LPS's I have (China made popular models) emit substantial magnetic interference from the body and some electrical interference from the power inlet area. I have no idea if this would affect the U16 ( I doubt it, the U16 and SU-1 have a similar magnetic signature themselves).
...but I usually distance my LPS's from source circuits (sometimes use a separate final regulator closer to the circuit) and audio cables, and/or use MuMetal sheets
Last I checked, 2 pcs of 1mm thick MuMetal sheets = approx. 18 CM of distance for magnetic, 1 sheet does a pretty good job eliminating the small electric interference.
But I doubt any of that is necessary, I often see manufacturers sales images showing power supplies stacked with components.
For temperature considerations, I am using a free-standing approx. 2.5A LPS for the GPS clock box, and the LPS is not generating excess heat - the top is pretty much at room temperature (sometimes 32C + this time of year). I have had similar LPS's get very hot under heavy current draw (ie. charging Uptone LPS 1), so it seems that the GPS clock is not pressuring the LPS much, but if you are stacking maybe an idea to consider a LPS with some extra amperage headroom and/or good heat sinks to keep temps under control.. and keep a little extra space between the components.