Warming up digital in my setup

Glare - that's a great way to describe what I'm hearing.  I'd like something that rounds off the edges :)  - even if it's an artifact.  I know this is all a bit personal choice, but I really couldn't tell a difference between sub 1k DAC (SMSL, Topping, Khadas).  In fact, the Khadas ToneBoard (v1) was the best sounding IMO.  Seems I might need to investigate $1.5k+ DACs?

USB cable is nothing special -- 15ft run - coming out from my iphone.  

I suggest looking at better speakers. If you really like the LS50, try the LS50 Meta. Much smoother on and off axis frequency response. In the same ballpark price-wise is the Ascend Acoustics Sierra-LX. Also measures quite nicely.

I see that distortion rises quite significantly with the LS50 (orig and Meta) when outputting high SPLs (~96 dB), so keep that in mind if you're really cranking up the volume.

Also look at the Border Patrol DAC. Very warm sounding and reasonably priced. 

My first thought it's your source. I haven't used an Iphone but USB isn't Apple's first choice of output and the USB cable length could also be a problem if you're trying to sit on the couch while listening.  I'm sure you don't want to hear this but it could also be a bad speaker / amplifier match.

I'm also an Amazon Music HD user and it sounds OK but not good Qobuz.  Saying that a lot of the music I enjoy just isn't on Qobuz so I dropped them.

+1 Soix regarding the MHDT Orchid.  It only outputs 16 bit but will accept 192/24 bit.  It was never a problem "sound wise" for me.

Consider reducing or eliminating speaker toe-in.