Thanks a lot guys! It is wonderful to hear from you on this.
on what Plowman and clarkcontrol mentioned, I admit I was very concerned about the repeated rhythms. So I only copied large sections in deliberately non-matching layers, never just one measure at a time, and played nearly all in real time. Except for the diabolical 16ths which Holst scored for ALL strings and woodwinds, in a totally off-the-wall combination of individually right but together wrong scales going in every direction during those hysterical sections before the slow middle part and at the very end.
Another thing I did that was a bit weird - on the col legno, which is scored for ALL STRINGS SIMULTANEOUSLY and which (understandably, being rarely used articulations) do not have a huge number of varied repetition samples, I had to use some cheating, since the number of repetitions was perfectly matched to the number of notes in the ostinato (arrghh!!!) --- I decided to do a randomly controlled crossfade between the slow and fast col legnos on all the instruments, as well as some unwritten dynamic changes to vary the attacks, which, if simply programmed at one velocity level, sounded like the dreaded machine gun times five (the number of separate col legnos).
also, on the section slop, I am trying to push it to an extreme. I remember once doing a slowed down re-recording of the New York Philharmonic under Bernstein doing a great performance of "Batuque" - a very rhythmic, spectacular showpiece. I could not believe how inaccurate it sounded, and yet when heard in context, it was a great performance by the (arguably, besides Solti-Chicago, and von Karajan-Vienna) greatest orchestra-conductor combination in recorded history. So I strongly feel MIDI performers have to "re-think" the entire concept of "accuracy" vs. "inaccuracy" in timings, not to mention tunings. Since we are seeing everything in 'slow motion" in a sense, by doing the performances from the ground up.