Stas,
Nice review of the 2500 x2! Rest assured, your Russian English-as-a-second-language speaks volumes better than most American English-as-a-first language. I have always strongly preferred (English translated) Russian/Soviet novelists. : )
FMOE*, I found the Proline 750 midrange to be much more immediate, intimate, involving, and less hollow than the 2500. In addition, the 2500 treble was more susceptible to grain and tiz than the (more treble-smooth) 750. The 2500 may have the edge with respect to bass balance, but lack the broadside thwack! and low end percussion of the 750.
The Proline signature, IMHO, is very direct and arresting--bordering on "forced entry," but more like a fine etching (like Leonardo's sketches) than a fine painting (e.g. Mona Lisa). It's like getting all the peaks from a topographical map, but not necessarily everything all the way "from the ground up."
"Somebody" really, really needs to do a comparison between the RAL/Proline 750 and the Ed.9. : ) Hint . . . Hint . . . However, with the RAL/K701 strapped on right now, I don't feel like I'm missing anything. Sure, you Ed.9-ers can sneer, while sporting your $1500 Ultrasone headgear, "Ignorance is bliss," but the phrase travels both ways! : P
(I'm secretly trying to incite someone to lend me their Ed.9.)
PAB
Key: FMOE=from my own experience