I have a pair of ESP-950s, bought them off Audiogon, the previous owner had put a Stax cable on them. He did a really nice job, it looks totally factory. There is some advantage to be gained from using the ESP-950's on the SRM-1/MK2 vs. the stock Koss amp. Bass is more solid and highs more refined. However, I find the overall sound less coherent than Stax- more colored, not as neutral. In some ways (bass impact, texture) I like the ESP-950 better than Lambda's I've got, but the Koss sound... well, just a little less neutral and not as coherent in the mids and highs. They are a good 'phone, don't get me wrong, and for $500~$600 worth the money.
Mine don't squeal.
I really wonder if drilling holes or adding / removing damping is going to make them sound better.