Speaking of Izumi's twitter, he dumped some extra lore on Refrain's 9th anniversary.
Amadeus was based on the painting 'Isle of the Dead' by Arnold Bocklin. Among other things, he confirms that's the inspiration for Bocklin's name, who "wasn't (?)" in Refrain.
I'm taking that to imply Bocklin is actually Newton, since he traveled with Mora and Furia and it'd make sense for him to still be working with Mezzaluca.