I know that the math says "No".  Digital sound is 1's and 0's.  Splat and SOP should sound identical until you start adding plugins, but I swear SOP sounds more "open".  Maybe I'm playing the SOP files a tad louder.  Dunno.  Anybody else experienced this?

Anything's possible.
 
It'll depend on how they're handling the summing in the busses.

Can merge this with the S1 sounds worse and let everyone duke it out :). But seriously, Jeff Evans has posted about comparisons between 4 DAWs using the same stems and the results were identical. He has posted that a few times now with the conditions of the test he used, stems only, no FX, and only L/C/R for pans IIRC.

That is true assuming there's no deliberate jiggery pokery going on.  Mixbus, for example, is touted as a software version of a hardware console and designed to sound as such.

People have claimed it sounds better than SPLAT. There were even advertisements on the Presonus site that basically have users saying "just sounds better". SPLAT was never named in those ads. 
 
I could have sworn it sounded smoother to me than SPLAT. Maybe the darker GUI played tricks on my ears.
 
In reality there was no difference and it was my ears/hearing and mindset that made me think this. This doesn't mean that the way the workflow works in the software won't lead people to make decisions that lead to a different sound, for instance, if my first and most accessible plugins in a daw tend to have a sharper sound we might infer the daw has a more harsh sound, when it was the tools we used and the way we were prone to use them. 

Debate going on forever and will likely continue avoiding the evidence. At the root core, do a null test from one DAW to the next. 180 out of phase and everything should silence. The DAW can only harness what is there behind the lines in the OS. If there is actually a difference, the DAW is suspect of not translating the signal without coloration.
 
However, when I get a dry audio signal from a guitar into Sonar, why does it sound so solid and rich, stable, present.
 
Magical faeries. Only answer I can come up with.
 
John

It can be a tricky thing
 

 
I can't get anything to sound as good as results I get in Studio One no matter what I tried, I have tried with SONAR Platinum, REAPER, Mixbus 3 and 4, but it's because of the use of Studio Ones Mix Engine FX's CTC-1 Pro Console shapper(extra paid for FX), which I find to be an awesome thing, or the included Mix Engine FX Console Shapper. It's not like SONARs Pro Channel as a lot of people seem to think, it's a completely different thing. Pro Channel is basically a glorified FX bin, 'sitting on top', Mix Engine FX is deep inside the audio/summing engine of Studio One, not just 'sitting on top' like the Pro Channel.
 
 

I once heard a Presonus salesperson actually say it out loud, and this is a direct quote: "Studio One just sounds better!".
 
That may be what put me off Studio One for so long. If the product demonstrator had no qualms about making such an absurd claim, then how could I trust anything else he told me? It also made me wonder: who is their target market? Gullible 16-year-old bedroom producers? Surely not serious audio folk who know that 1 + 1 = 10.
 
(Unless the + symbol is being used as a logical OR, in which case 1 + 1 = 1)
 
Fortunately, I got over that prejudice and can now respect Studio One for the quality product it's become. But to this day, whenever I hear such nonsense my mind snaps back to that demo and that over-caffeinated salesman.

Presonus say all sorts of stuff in their marketing gumph. Some people are saying it sounds better and some are saying it sounds worse. It should sound the same. I am assuming they are using 64bit processing, the same sample and bit rate and the same plugins in both to get their comparisons, but then again I assume not. :)