Searching for a little more warmth

In my experience most rooms tend to be on the bright side. Have you considered room treatments or some type of equalization?

Nice equipment. Well, the amp and preamp.

Ok. If you are like most of us, then you sit and enjoy listening to music. To do that you set up your speakers 6 - 8’ apart and position your listening position to make an equilateral triangle. Then with lots of small adjustments the whole soundstage snaps into place. The triangle can be bigger with really huge speakers and powerful equipment… the exact opposite of what you have. You have some of the most coveted warm - natural sounding equipment on the planet. So, much discussion on the setup needs to take place. Photos would be really useful… there is a place under your userID to create a virtual system.

Next, the BlueSound is outclassed by orders of magnitude by your main system. It’s like you are using a transistor radio to feed it. Your system deserves at least an Aurender N20 or better with a high end DAC… I am a big fan of Audio Research DAC 9 for it’s warm natural sound that would complement your main system.

Yeah, the midrange-forward, bass-light Zu coupled with 300B can't be filling the room that well. A pair of subs could help and will add to your system even if you change things in future. New DAC per @ghdprentice may also flesh out the music. 

@croissantfoxwine I know the Soul VI is a much more advanced speaker, but I owned both Tekton and Zu Soul Superfly speakers many years ago, powering both with low power SET amps. In my experience it is a real challenge to get a lot of warmth out of Zu speakers. The Soul in particular is a fairly small cabinet, and you have a medium-to-large sized room.

In fact, if you were to keep your amp and preamp, which George has already noted are really nice, you will likely have to invest in potentially bi-amping your setup, where the Shindo are powering 120-140Hz and above for a speaker, and you get more powerful amps for the lower frequencies. 8wpc in a room that size is very limiting if you plan to power the bass and midbass. But adding subs won’t necessarily give you the warmth you seek, as the Zu Soul are just not a warm sounding speaker. 

Devore are definitely a little softer in their presentation, as are Audio Note speakers. Fyne Audio may also be another to consider. Horn-based speaker systems may be best, where the bass drivers are driven bi-amped with a cheaper Class D amp. 

The rest of the community may have better speaker recommendations as it’s been a few years since I’ve done anything with low power and high efficiency.