Thanks for the reply, Phil! That's good to know. In both of those clips the mix was set to 53%. Here's a clip with the Helix set to 100%, but it still doesn't get there. To my ears, it sounds like the modulation/depth on the echos isn't as extreme, and there's less swell time available on the "dry" signal.
https://www.dropbox.com/s/axfbzqhd04kkf8i/auto_volume_test-3a.mp3?dl=0
for reference, here's the same clip through an M-series pedal at 50% mix
https://www.dropbox.com/s/ojz93w948a67k0b/auto_volume_test_M.mp3?dl=0
and the same clip going through a DL4 at 50% mix. Output seems to be a bit hotter than the others, but aside from likely differences in a/d converters, this sounds more similar to the Echo Pro-
https://www.dropbox.com/s/6brgpful9ljyr8c/auto_volume_test_DL4.mp3?dl=0
For what it's worth, I've spent some time in the studio with 2.50, trying to dial in the same sound without looking where my hands were on the knobs, but I just can't recreate it.