shiit Freya+ muffles the base? Recommendation for preamp please

Try rolling in some better tubes. NOS 6SN7's have a more extended low-end.

http://www.audiotubes.com/6sn7.htm

ARC, Supratek, EAR, Atmasphere…

"muffles the base"

That's interesting. But how is the bass?

Are you using balanced or single ended connection?  Those two may be a mismatch, given the impedance matching:

https://forum.audiogon.com/discussions/amp-preamp-impedance-matching-can-anyone-explain

Check the specs, but I think if you use XLR connection you should be okay?

I have always liked the sound of B&W. So I recently upgraded my speakers to 804s.

...Strangely, the bass was not satisfying or full enough for me, even though it is a big speaker.

...Again, here, the bass was the weak point.

...it was the deeper bass that was lacking.

...if more bass is desired, add a nice subwoofer.

....It was only at very loud levels that the bass finally shone through.

...the only area I found lacking was the bass output,

{Editors note- The 804S does not have a lot of distortion in the low frequencies, and depending on what one has listened to in the past, the 804S’ lack of bass may just be a lack of distortion. }

But what the heck, it must be the Freya that is at fault because of reasons and "I have always liked the sound of B&W.".

After all, Freya’s specs are only 3Hz to 200KHz -3dB in tube mode.

Edit - I haven’t seen any test how Freya+ output impedance behaves at low frequencies. I think - and I am happy to be corrected - that this may be an issue with tube pre-amps in general, but depending on design.