Tube Buffer between cdp & pre

I use a 'tube buffer' between my DAC and preamp. I tried a new Bryston DAC and it was no better than my old Adcom DAC 'in my system'.
My digital is not as good sounding as my analog stuff.. So at first a tried an inexpensive Chinese buffer. It did a little. Then I had a chance to buy a VAC Standard preamp (it uses four tubes). i use the VAC just as a tube buffer between the DAC and my preamp, a Bryston BP-26. The VAC works great to tame the digital.
Might be a little expensive for just a tube bufer, but it is what I use.
(My VAC Standard is not as transparent as the Bryston BP-26, which is better with the Phono stuff, and is the balanced out to my Bryston amp.

My digital source Blacknote DSS 30 has a built in passive volume output, so to better match the impedances I use an Audio Horizons TB 5.0 tube buffer in between the Blacknote and my amp (W4S ICE amp). Without it the highs are somewhat reduced and it doesn't sound as good.

I have a MF tube buffer inserted between a tuner and Sony es receiver( not using internal tuner as it is very poor).I think it improves the sound considerably, with smother, less harsh highs I would like to try it for CD's without loosing the tuner. Can I use tape in/out on the receiver, and exactly how?