These mics. have been made for a long time and they're still available, that should give you some kind of clue. I never hear anyone talk about them much. I like the 260 for overheads and HH, I have 3, I have 2 JV74's for trumpet, fluglehorn, Ac. Gtr.. but the 160 works too and sounds cleaner (hypercardioid). I've never had a problem withguitar amps, it's better if you put them in a dog house for some reason. Depending on what type of sound you're going for, they work great for piano too. The M500 was Ol' Blue Eyes live mic. Sounds good on voice, trumpet and alto
Generally you need really quiet mic. pres. with lots of gain, but now Royer makes an active ribbon. Another ribbon is the Coles 4038, bidirectional. The Beyers sound great and they're cheaper. I've had mine for a while and I've never heard of the mod. What does it do? Where can you get it done? Any info would be appreciated.