I've seen it done before quite a lot of times (offline). I used to mod everything I own incl. musical equipment for better filtering, bandwidth and sound quality, and caps were easy so they came first.

Where'd you pick up the Rubycon Black Gate NX from Janus?

Why didn't you opt for Philips Low Loss (Q LL) caps?
They are what is used far often in the best musical equipment (amps too), have higher and tighter tolerances and frequency bandwidth, temperature tolerances, life and quality. Pair them up with Black Gate FK for best results.