Totally agree with you about there being a lack of rhythmic clarity in PMD's 1st. It's just too formless and nebulous to fully grasp onto. Have you heard any of Max's symphonies after the 3rd? I've only heard the first three-they seem to get progressively better from the 1st.
I found the 6th mostly long and dreary, though there was a striking passage for high trumpets near the end of the first movement. Haven't heard 1 through 5 though, so no basis for comparison. I do find it somewhat astonishing that someone can be a professional and highly regarded composer for decades without ever developing a good sense of rhythm.
Anyway, heard Shostakovich 11 ("The Year 1905") last night—second listen ever. I think my first experience with the work must have been a rather inferior performance since I found it a much more compelling piece this time around. It's less of a symphony and more of an extended dramatic tableau, so purists might take exception to the title, but I do think it is one of DSCH's better works.
Next on the list are Symphonies 2, 3 and 4 in some order, & possibly a revisitation of
The Nose, though I find Shostakovich works best for me in small doses >.> so might be a couple of weeks.