According to the Sound Devices web site the USBPre2 have the same Pre Amp stage as the SD 702/722/744. Thus I would think it would be wildly different in sound to the PSP-2 (since the PSP-2 uses input transformers).
I ran both the SD702 and PSP-2 for a while and never liked the SD702's pre-amps (very thin and shrilly) with my various Schoeps (both m222 and cmc6xt's and various caps) - and endded up getting rid of the 702 as in my mind it was not an all in one solution for my mics.
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