New Preamplifier Testing (Poor sound)

Looking for help...

I got a new preamplifier to replace my integrated amplifier, but the sound is extremely underwhelming. Biggest issues are sound distinction and clarity (sounds dull) and field depth (sounds narrow/flat) with less depth and width regarding the sound field when listening to stored digital music.

Old set up:
Innuos Zenith -> (USB) Gustard X26 Pro -> (XLR) Cambridge Azur 851a -> (RCA) Cambridge Azur 851w -> KEF LS50 Meta's and Kube 12b subwoofer.

New set up:
Innuos Zenith -> (USB) Gustard X26 Pro -> (XLR) Rotel 1590MKii Preamp -> (XLR) Cambridge Azur 851w -> KEF LS50 Meta's and Kube 12b subwoofer.

I'm really surprised this new preamplifier was such a drop off in sound quality compared to my older, cheaper integrated amp, but wondering if there are any tests I could do to maybe change something to better figure out if its the preamp, or rather something I'm doing. Looking at all the extra digital inputs in the Rotel that my 851a doesn't have makes me think that maybe the 851a is just a more adept component at passing along my DAC's signal, where the Rotel is geared towards using it's internal DAC.

The Rotel is run in a "Tone Bypass" mode via the XLR connections to bypass the internal DAC.

Just wondering why the Rotel would choke off the sound so much while the older integrated amp make things sound so deep and bright when paired with the power amp?

A friend suggested running my DAC straight to my power amp and see if the sound was back to old (or at least better).

Any other suggestions I should try before I send the preamplifier back?