Shouldn't it be crisper/cleaner/more vibrant?

I've never known any Klipsch to be "bright and clean."  They're efficient and play loudly with deep bass, but IMHO, they're not transparent, holographic, and don't disappear--which is fine if that's what your after; however, if you want a clean, sparkly highs, with a holographic mid-range, then you've got the wrong speaker. . .then again, what do I know, I've had to same speakers for over 30 years.  

What is your listening environment like? The room is half the sound, so if you leave out details about the room, you're inviting pure speculation or reports about other systems in rooms that could be very different than yours. Maybe that's all you want, though. Unless you're trying to answer a real question.

I'm not familiar with your amp, but I have owned Cornwall IVs and they are very capable of what are looking for. As @hilde45 mentions, your room might be the issue. Also I would question whether a streamer/amp combo would give you the best results. The Cornwalls love a tube amp and ultimately, that's where you should be IMHO.

It should certainly be crisp and clean with Klipsch. Not sure that you will get vibrant out of an all in one Class D setup. I don’t want to go too far down the cable rabbit hole, but what are you using for speaker cables?