The samurai vs Cho fight scene was probably the best thing associated with Sumi and Taka, so we wanted to have an excuse to feature it, and made them as sort a tie-in/reference to Alucard's future interest in Japan and its anti-vampire secret agency. lol
When we did some private test screening, we had a single "too much music" complaint, but I believe Castlevania with no music is like bread with no butter - it can be watchable, but music helps a lot in setting the tone and makes the scenes more memorable.
Yes, it was one of my earlier ideas - Trezire de Spiirit is one of those themes associated with Trevor (since he was the protagonist in most CV pachislots), and the song lyrics fit really well with how the heroes are "entering the Devil's palace".