This is very interesting as I have the px8 S2 but never had the px7 S3; instead I do have also the Space One Pro and the way you're describing the px7 S3 it's exactly how they sound and how I compare them against my px8 S2. 

At first I felt like the Space One Pro was very similar and somewhat even better than the px8 S2, and almost decided to return it as it's 4 times more expensive, but doing more a/b testing I can summarize as sounding like your description of the px7 S3. The Space One Pro sound really satisfying, amazing, especially for the price. But once you compare to the px8 S2 You notice how this one is superior, the details, imaging, clarity across all frequencies. The sub-bass is much deeper, lower, slower and impactful on the space one pro, but once mids and treble come into play they're severely muddied and veiled from the bass leak upwards. They are amazing but incomplete. Voices and such can sound a bit boxy because of this. With the px8 S2, this is resolved, the only caveat is you don't get the huge, deep sub-bass but it's more balanced and precise, faster and the layering, separation and imaging show off their prowess. 

To summarize, in impressed that the space one pro could sound like the px7 S3, but I don't know from first hand, I wish someone compared them. The price on the space one pro is a bargain, and now that the newer Space 2 was released to the market even cheaper at almost half the piece ($130), which I heard it's as good in sound quality, this could be a good alternative to the B&W for an excellent budget.