As anyone who has ever arranged a string quartet for string orchestra will tell you, the biggest problem is trying to get an orchestra to play as quickly as a quartet. Ask Mahler about his arrangement of Schubert's D minor String Quartet. He'll tell you that it was no problem getting an orchestra to play the opening hard enough or heavy enough; the problem was getting them to play the opening fast enough. There's a simple reason for this -- an orchestra with more than one player to a part just can't make the same speed as a quartet with one player to a part.
Ask Victor Kissine about his arrangement of Schubert's G major Quartet. Ask him if the lugubrious tempo that Gidon Kremer and the KREMERata BALTICA use for the opening Allegro molto moderato or the weighty tone they use for the central Andante con poco moto is really appropriate. Ask him if their articulation of the following Scherzo or their phrasing of the closing Allegro assai is really apposite. If he tells you it is, he's probably kidding. Or, better yet, ask Schubert. While he might be pleased that so many people are interested in his music, he'd probably be disappointed that they're not playing it the way he wrote it. ECM's sound is clear, deep, and warm.