Richard - Here's a link to a page describing APX 25 in very dilute Rodinal:(posted 9003 days ago)http://www.slonet.org/~dkrehbie/2photo/film/develop/develop.htm#rodina l
This site was done by Don Krehbiel, an expert photographer and utter master of getting downright AMAZING results with tiny Minox negatives. His entire site is worth checking out, quite informative and interesting.
And regarding Microdol-X, I used it 1:3 with APX 100 shot in my Minox for a year or two. The results were mixed: the grain WAS absoultely wonderful - very tight, invisible in 4x5 prints from Minox negs - but in other regards, the MicX wasn't so hot. While I never experienced the infamous "loss of film speed", the negatives were mostly very flat and lacking in contrast (I had to use a #4 filter for nearly everything). What's more, this particular solution had a much higher level of crud in it than anything else I've ever used (DK-50 for sheet film, D-76 and XTOL for smaller formats), and the negatives were frequently ruined by bits of undissolved chemical grains, dust, tiny hairs, etc., which adhered to the negatives and wouldn't wash away. Plus, the MicX had a very short lifespan once mixed - only about 10 weeks before it suddenly went bad - so for the miniscule amounts I needed for Minox work, I ended up throwing quite a bit away. But the grain WAS excellent...
XTOL is probably a better bet these days. Personally, call me old- fashioned, but I still love good old D-76 1:1, and use it for nearly everything!