Your custom sound is excellent! I feel like the older samples from Sibelius (pre 7) had the right idea: an impression that made it easy to imagine the choir was singing any vowel or articulation. This is pretty close, and in some ways even better. It sounds much more natural than virtual instruments that try and simulate a “real” choral sound. Which Logic Pro samples are those, and did you lean more on one side or the other?
I’m still surprised there isn’t a built in option that’s just a really good synth voice, given that it’s been done before.
Logic/Garageband has a “Mixed Choir” and a “Classical Choir Female/Male”. I used the samples from those, which are just aif files, to create instruments in ARIA Player. ARIA instruments are just text-based SFZ files that describe the conditions for each sample file to played. (If you open the aif file in Audacity or similar, the loop points are saved in the file.)
So, my Sopranos use Garritan GPO5 Sopranos, plus “Mixed”, plus CC Female. Even though it’s three separate sets of samples (and I configured one of them to change vowels each note), it’s still quite lightweight.