Nonsense. They are birds of the same feather as described by Eventide themselves. You are just subdued by subtle differences, and that matters to you. Whenever people start talking about faithfully reproducing filters in the A2D chain I'm pretty sure that we're in grey town and I'm not much going to care.
Isn't Dan Gillespie from Eventide? He says:
The 2016 Stereo Room plug-in is a recreation of the Stereo Room algorithm only whereas the SP2016 recreates the Room, Stereo Room, and HD Plate algorithms from the original SP2016 hardware box. The SP2016 Reverb plug-in also more faithfully recreates aspects of the original hardware like the filters in the converters, the bit rate, and sample rate which make it a very faithful recreation of that wonderful box.
In other words, the 2016 Stereo Room plug-in is a really great reverb algorithm in a plug-in while the SP2016 Reverb is like having a really rare piece of very dank hardware in your DAW.
So, if you don't like the plate, and I don't, then you have two room algorithms that are mono/stereo versions of the same algorithm that is in the original with some better modeling of bit rate and A2D filtering.
It's not that interesting enough of a sound, for me, that I need two reverbs that approximate it. I think that the upshot here, to my ears, is that it's a recreation of old algorithms. So, there is some limit as to how good it's going to sound in the first place. I'm not sold by vintage digital, especially not on the subtle details. The original Stereo Room was never going to replace my much better modern reverbs, I just liked it for its particular flavor some of the time, in much the same way that I like NI's RC24/RC48 or PSP2445. In fact, while I can clearly hear that the "modern" flavor sounds less like it was from the 80s, I don't think that it improves those old algorithms enough to justify it's use.
I'm not saying that it's a bad product, I just don't care. If you had neither and had to get one, you should probably get the newer one. If you have the old one and you want to spend $29 on reverb, I think that there are better ways to spend it that you will get more variety and more bang for your buck. Waves Chamber, for example, or put it towards UVI plate, at least that sounds like a plate. I wish that I had not bothered with this and just waited until it was in the next bundle upgrade that had other products that I do care about. It's certainly not interestingly different from Stereo Room like Blackhole, TVerb, Ultrareverb, etc. are. Those are reverbs that give you a variety of sound. Those sound "different" and will continue to sound different in the mix.
In any case, IMO, it's certainly not worth the intro price, let alone the regular price. Keep in mind here that I paid the $99 intro price for T-Verb and don't regret it. I would have liked it a LOT better had they put it in the Blackhole style interface and given it the ribbon. Then you could modulate the position parameter with other parameters at the same time. I'm not a fan of vintage U/I recreations when the U/I serves no real purpose in a modern age. This isn't always true, but it's true here.
As far as preferring the sound, it comes down to taste, I don't like the modern 2016 sound in this plugin, but I don't like R2 either, so there you go. As far as whether they sound really different, bullshit, that's exaggeration and hyperbole. They are models of the EXACT SAME VINTAGE DIGITAL HARDWARE, so of course they don't sound all that different.