I grew up with many of the Quartetto Italiano recordings, beginning in the sixties and seventies. Recently when one of the tape sources let me know that he had the complete Beethoven String Quartets and the Mozart "Haydn Quartets" with the Quartetto Italiano, I couldn't resist. I added 20 new tapes covering the Beethoven Quartets, 6 more for the Mozart, joining the two tape Brahms Piano Quintet with Pollini and the QI. It is very obvious that the recordings on Philips do not do the QI justice. The tapes have a much greater dynamic range and go both much lower in the bass (the cello growls) and higher in the treble (the shimmering strings). Philips' reputation of rolling off highs and lows to make tracking easier is shown to be well deserved.
I never saw the QI in person (I did see the Budapest SQ in the mid 60's in college with 18 year old Peter Serkin playing the Brahms Quintet.) Although I was an astronomy major in college (with lots of math and physics) many of my electives were in music, including one semester focusing on Haydn and Mozart String Quartets and the next semester on Beethoven Chamber Music, including all the String Quartets. These were both upper division classes aimed at non-music majors. We even had enough string players in the classes to have two different string quartets (except for a viola, played by a faculty member), one for the easier quartets and one for the more difficult. What a great time for education.
Larry