Pink Floyd's Echoes might be my favorite song ever, so just wanted to weigh in on the Theme jam from that angle. Echoes has 4 basic sections: an epic/dreamy beginning, a dark funky groove, some ambient wailing, and an epic/dreamy ending.

In Theme, just after starting the "from the bottom, from the top" vocal rounds, Phish begins playing a dark funky groove. It seems like this was planned; the whole band is right there, no one is still playing Theme, and the vocals are quickly abandoned.

So is it the dark funky groove from Echoes? Well, sort of. Floyd's version is much sparser. Fish and Mike embellish a lot more and give the whole thing a more bouncy, upbeat, danceable vibe. I'm listening and about to write the Echoes similarity off as superficial and coincidental... when Trey plays a few Gilmour guitar lines, note for note. Ah, okay, they ARE playing the second section from Echoes, just in a very filtered-through-Phish kind of way.

Apparently not recalling where the Echoes solo goes from there, Trey repeats the same phrases a few more times before the jam nicely segues into Steam.

So that's the scoop; seek it out or not as you see fit. Personally, I enjoyed it, but more as a brief moment of "well that's nifty" rather than any sort of epic event.