Upgrading pre amp advice.

I know if I were in your position I would sell/trade-in your DAC and preamp for a DAC with volume control. That is, if digital is your only source. The value and sound quality is way better that way, in my experience. 

Take a look at Audio Mirror Linea preamp. Tube, balanced XLR in and out. High build quality with great support from Vlad at Audio Mirror. Fantastic value. Should be able to find used in your price range. 

@easystreamer : did you see my question (https://forum.audiogon.com/posts/2868242) ; )

Do you have experience with this device?

@deep_333 : didn't know Onkyo still existed.

@abd1 : I would like to know why the control amp section of the MU2 is so great (how did they do that without using tubes?) @ericrhodes1 : yeah, there many users who are feeding their Class D power amp with a tube pre amp, the advance can be adjusting the sound by swapping the tubes but many of the preamps mentioned are hard to get in Europe (and it will be a new start for me). It would be nice to look around if there is somebody I can ask to try for some hours/time??

I have owned more amp and preamp combinations than some of you could imagine.  Some of the best from Krell from FPB to Evo to Evolution 1&2's Classe Omega series, Pass Labs XO.2 w/ XA200 and x600, Melos MAR 333 & MAT 1000's Viva, Bryston, Counterpoint, Boulder, ASR, Rogue, Rotel, Joule Electra, VAC, Conrad Johnson, BAT, Jadis, VTL, Threshold, Audionet, Carver, Accuphase, Yamaha, Audio Research and yes Benchmark.  I have had well over $1M invested in my systems after starting of with a $1k System in 1979.  So I know the upgrade cycle.  What I can state is that synergy between components is key!!!  Output impedance to input impedance plays a big role.  My current system is using an upgraded BAT Rex 3 preamp.  The upgrade was done with input from BAT themselves.  I have helped and collaborated with friends that now have a new lease on their BAT gear.  You can find a vk51se or vk32se in the mid $2k range new.  Upgrade the caps with Vcap ODAMs.  It will be a revelation.  The Benchmark just does not have the musicality of what either of these preamps can do with the ODAMs installed.  Here is a quote from a friend who upgraded his Vk51se:

"Well, can it be? Must be since I’m hearing it. Your setup is one thing but mine is OK and I have evoked with it so I know what the cables and etc do. I know what all my setups did and didn’t do. The C3 with the 27.5 and 51SE was special. Added the 5302 and it became tauter and more lively wider soundstage. Now I’m using just the Focal 7” two way with Tdx90 tweeters. Nothing phenomenal but they are hand silver soldered high end crossovers. Well. What is happening I don’t know and cannot describe. It’s the first time ever literally that I got lost in the sound stage. The bass was surrounding me. The treble washing across the back the vocals the vocals are making open my eyes make sure no one is in the room. It does feel a bit peaking in the upper mids by the slightest amount could be room placement or the tweeters. But the sound has gone from analog to digital to now just real pretty much. With the bass extension of the C3 it would be real. John there’s no words. The setup used to be right now it’s breathing and alive really. Hard for me to fathom, just caps? Wow it’s astounding. Like someone took off the brakes. Thank you!!!!!!!!!!!!!!"

Well Worth It!!! A budget friendly hidden gem of an upgrade, all in for under $3500.  You can call me if you like. +1 917-304-9800.  I have been here on Audiogon since its inception.  Just trying to help.

@vip428 : thx for your exhaustive answer. I take it from you that the BAT amp is the best for you, but which of the brands you owned came the closest to the sound? Pass Labs, Bryston, Conrad Johnson, Accuphase, Yamaha, Audio Research, Benchmark, Krell?

By the way I did a search on BAT pre amps and found this one : some found BAT rather dry and suggested 'warmer' combination???