Apologies for double posting so soon after this thread was created, but I was asked elsewhere about the other
Im@s connection(s) to
SPiKA:

As noted
here, Rion herself is voiced by Manami Numakura, who of course voices Chibiki (and her non-puchi counterpart). Although her design seems to have more of a Mika vibe about her, in my view.

These are the other two members voiced by
Im@s alumni:
Haruna (the one on the right) is voiced by Aya Suzaki (AKA Minami Nitta), while
Reika (on the left) is voiced by Ayaka Suwa (who also voices Matsuri Tokugawa).
So that makes one "original"
Im@s voice, one from
CG, and one from
ML.

So far as I'm aware, the VAs for
Wakaba (Ari Ozawa) and
Akira (Mutsumi Tamura) have not appeared in any
Im@s-related media as of yet.
Falcom will be releasing
a mini-album with three of
SPiKA's in-game songs - one of which is reported to be the theme song for a show-within-a-game,
Mahou Shoujo: Magical Alisa. (A sample of another song,
Seize the Day, is in the recent five-minute game trailer.)