Interesting - great to hear from someone who tried a different chip. Personally, that doesn't seem like a huge surprise. Theoretically, at least, opamps shouldn't really be adding much "coloration". Granted, Jimmy J is absolutely right that Alembic uses ones that are high-quality, even among audio-grade opamps! (They just consume more power.) And as Keith noted, some of them do make a difference. But my general impression is that it shouldn't make nearly as much difference as (for example) changing the transistors in a Fuzz Face pedal, where those components DO make a big difference to the tone. There are probably dozens of popular audio-grade, low-noise opamps out there that are "close enough" that the audible difference is negligible.
I think the biggest credit for the Series 1/2 sound is to Alembic, not the individual components. E.g. even the Series 1/2 high-grade opamps are only ~$1 each in bulk. I bet Ron Wickersham would probably agree that the "magic" is in the DESIGN of the circuit, not any one "magic" part!