Probably an old debate, but I haven’t heard both products.
Audio Bacon described them both as follows a few years ago.
Is this still true with the advances in both camps, particularly with the introduction of the OpticalRendu or are they closer together now?
A few years ago probably wouldn’t be a fair assessment given technology advancements. Sonore is very active here. I’d reach out to @agillis at Small Green Computer for the tech aspects. He’s very helpful and sells the Sonore and other high quality music networking gear.
No one, but you, can decide how something sounds or which sound you like better.
Particularly with descriptions like this -
This kind of poetry is how reviewers make their livings, but I’m not sure it’s much use in deciding what device you like best.
I wouldn’t put too much faith in those descriptions. In any case, all reports are that the new
Sonore optical units are another step up.
I’d suggest you concentrate on two other areas: the user interface and customer service. Sonore is known for regularly updating the OS and UI. They also have personal service, to the point of logging on to your unit remotely and fixing problems. They once installed a specialized version of a driver for me, just so I could use my DAC with their unit.
Good luck getting that from SOtM. And I have bought SOtM products.
I don’t have any SOtM products, but I would echo danny2’s comments about Sonore. Jesus from Sonore offered to log into my microRendu to resolve a problem I had trying to get a bit perfect stream through to my DAC for MQA processing. He resolved the problem almost immediately. Fantastic customer service.
I can even find it a bit amusing how two bit perfect (i very much hope) transports can have different tonality! 
Still, I do hear differences between my Raspberry Pi’s, the Allo USBridge, SOtM sMs-200 and the Auralic Aries. They are more of a “cleanliness” kind though…
I have an UltraRendu + Uptone LPS-1.2 and compared to the Mac Mini it replaced, it definitely has more resolution, but it can be a little too clinical and sometimes even grating in the very top registers.
If I were to use analog analogies, it’s more Lyra than Koetsu.
My analog rig has run Koetsu for almost 20 years into tubes.
I prefer a warmer, musical presentation to a clinical one, but that’s my preference.
If, indeed, there are differences in sound to the streamers (and I think there will be, just like there are/were in CD players and DACs for that matter) then I am curious to try SOTM because it sounds like they have that warmer presentation.
Last night I added a galvanic isolation stage using fibre, and while it made vast improvements to the soundstage, layering and depth of the image, that slight glare at the very top persists 
I’m not certain that this would be removed by upgrading to an Optical Rendu.
Thanks for the more accurate description.
I’m guessing from how you’ve described your tastes that the slight glare is just how you hear things. Everyone hears differently. Or you have something else in your setup/room that is causing what you perceive as glare.
The Rendu stuff is designed to be totally neutral and I think it is very close to that. So either you are hearing neutrality and don’t like it (I think most people actually don’t); or something is adding glare. I doubt it is the Rendu system.
The experiements at Harman showed that both trained and untrained listeners prefer a result with a sloping downward response - and actually perceive that as “flat”. A true flat in room response is perceived as too bright.
@danny2
Yeah, we are creatures of habit.
Probably why I love Koetsu.
Colored? - yes, a little, but it has a magical midrange presentation that you either love or hate.
Nothing in the rest of my system adds glare.
Analog sounds fantastic and very natural.
The only thing I changed with the UR was the addition of a very small Curious USB cable.
I’ll try switching that out before I go any further…