Give it some time. You made a number of changes at one time so there are many variables here. I generally try to make one change at a time. I've never heard this exact issue you speak of with the Cast caps, don't recall tonal balance being an issue.
Duelund cap break in time
I just made some changes to my single ended kt150 amplifier that I was pretty excited about, having had great success with similar mods to my preamp.
Unfortunately, when I set it all back up...it sounded worse. Not terrible, but worse.
It sounds extremely bass heavy. Overwhelming. Less detail, zero "sparkle". Dull.
I run this amp on my wideband driver - 500hz and up so that's extra confusing, it must be super bassy in the 500-1000 region I guess.
Now, I've only got about 6 hours on them so obviously there's a lot of break in needed, but every piece of equipment I've ever had (including cap changes)the initial impression was grainy, a bit harsh and shrill. This is the opposite, it's so smooth it's boring. So that's why I'm sorta baffled and feeling like I messed up, or messed something up in there, it's just far from what I would expect.
Is this level of dullness... reasonable? Happy to hear any thoughts on this, if it's entirely reasonable I'll just settle in and give it hours and try not to focus on it too much.
Changes made were:
Kle perfect harmony RCA jacks
Neotech silver gold hook up wire to RCA
Audio Note input coupling caps
Duelund cast pio hybrid coupling caps.
Focusing on the duelund because it's the biggest change but...