I've just read this thread through from the beginning. Several variables being mixed together here, and in the context of the OP's starting post, some variables that I don't recall being illuminated. Such as room size and shape, treatments, power conditioning, other system components and so on.
To the OP, cables and power cords may or may not be at the root of your concern, but there is no question that proper tuning using them can help. With my own largely Bryston system, over the past 14 months or so I've invested time and money in tuning via cables and PCs, and along with other setup refinements, I've gotten some very good results. What I've been hearing with each change, sometimes better and sometimes not, has been verified by two friends who hear my system frequently, one of which is also a life-long industry participant. Both have confirmed hearing essentially what I have.
I have a BP19, BDP3,BDA3, Bryston amps & T10s in active mode.
I've found that four figure costs for cables aren't necessary to tune a system. Having tested a few options, I've settled on two brands for their generally very good potential for good SQ, good value, and that generally avoid the symptom of a perceptual increase in detail and the expense of natural tonality and musicality. System synergy is also a factor, so what works here may not be what you need.
Oyaide and Mogami. Mogami is largely focused on pro, stage and studio, but have a few exceptional offerings that can work well in residential systems. Oyaide, at their core, are expert at metallurgy and construction geometries, and have some of the purest sounding copper-based cables. Currently my interconnects are mostly Mogami, as are my speaker cables. For now, I've settled on Oyaide for PCs. (I won't name the "audiophile" brands that have been replaced by these.)
My point is that, while good setup has to address every aspect of a system, it HAS to include suitable after-market cables and power cords. Many after-market power cords share the all too common problem of other cables, i.e. some great qualities but marred by an emphasis on upper mids and lower highs that can make a system sound a-musical (although impressive on initial listen), unless your system happens to be recessed in those bands, or your room over-damped etc.
The discussion of MM vs. Roon etc. is interesting. I use MM with a local library, and I don't use internet streaming, so I may have a blind spot there. Apart from convenience, I haven't been impressed with either Tidal or Quobuz streamed sound quality. My friend keeps telling me I should try Roon. I'm waiting to hear what Bryston may or may not be about to introduce.
Not sure if this helps, hope so.
Brian