Could you comment on the difference your finding between the EP weich, and the new Poly chromes.
I've had the Polychromes on for about a month now. But I should also say that I've been experimenting a little with them in combination with other strings (Spiro mediums, Sweichs, EP weichs on the bottom). Now I'm back to a full set of polychromes.
On my bass (2003 Schnitzer/DeSola, spruce top, ash back & sides):
Polychromes are springy out of the package, but play with less tension than EP weichs.
They have a soft feel under the left hand.
The set has good balance (in terms of tension and consistent volume), although for the first few weeks, the A & E were tighter than the G & D (hence the experimenting with Spiros, then EPw's on the bottom). With more playing time, the A now feels more like the G & D and the E is starting to head in that direction. (Maybe like what I've heard about Zyex, they just need some time to work out their kinks.)
Dark sound, yet good clarity in the pitches.
Less sustain than EP weichs, but a solid output with a tighter low end response. EPw's sound more "modern" (growl, more mid frequency content) in comparison. Polychromes sound more like 50's Blue Note, or 50's Sinatra.
Just as loud as EPw's, and they have a higher dynamic ceiling than EPw's. (They just seem more robust in general.)
Very smooth & easy to start under the bow. Like their pizz sound: dark, yet good clarity in the pitches. For arco, I like the polychromes more than any other synthetic string - by far. A legitimate arco set, particularly for (I'd imagine) orchestral work. EPw's are more coarse in comparison (esp. in thumb position).
Bottom line? Big, dark, solid sound. I like 'em.