Don't take my comments as a negative.
I do not lean toward a Rich Presentation where there is a perception to my sensitivities to the Bass Frequencies as being Warm.
I am happy to experience a Perception of Richness that leans away from a perception of being transparent.
Your description of a sonic that is to be experienced suggests that there is a wish to have something that will soften the impact of the delivery of sound.
This could be achieved by the Speaker, but could also prove to be the most costly, and if achieved through a Cabinet Speaker the coloration from the Cabinet that is detectable to some sensitivities, might not be overlooked and always a repellent and not wanted.
Approaching the change of sonic from the Phonostage end, will be a period of Trial.
A Valve Phono Pre' will supply a Harder or Softer Edge, depending on the Valves chosen in the circuit.
The use of Valves will also enable a simplistic method to change the sonic, as the exchanges are relatively easy to achieve by a user of a device.
A Valve Phono Pre' that I am quite familiar with for more than 20 Years and have not owned is the EAR 834P, this in my encounters of it as a Original Spec' and Clone Build has been a Warm Presentation, quite a few increments beyond what I would class as Rich in Presentation.
Another Phono Pre' I have been demonstrated that has shown a overly Rich Presentation, bordering on Warm, in the system it was demonstrated in is the Modwright SE 9.0. This Phon' got my attention and I could not think of anything better to try in the Home System through my ESL Speakers playing Chicago Blues music. Again the MM Stage is able to be Tube Rolled to an individuals taste and unique preference.
Keep in mind a Standalone SUT will add a hint of Richness to the point of being detectable as Warm. There are recent posts on here about SUT's and how owners of models perceived the presentation. This might be a very simple solution to the requirement you are investigating.
Before any of the above is put in Place, I would try out a D.U.C.C Wire Cable in 6N or 7N Purity. These Cables are extremely clean/revealing and allow a substantial amount of information to be rendered that other Wire in Cables fail to manifest.
In relation to other Wire such as PC Triple C, used for Cables that have similar capacity to be clean/revealing and render detail that is not commonly encountered, the D.U.C.C has a hint of Richness, there is a perception of a weight added to a Vocal Bass Note and Wood Wind Instrument when in use.
I would recommend D.U.C.C Wire as Cable to anybody wanting to discover a little meat on the bones and not smear or destroy the micro details from a recording.