There a LOT of VERY expensive amps on the market. In terms of how loud they go? Any good amp will probably drive most speakers past what is considered normal listening levels. I don't know if you've done any dB checks, but most of the time I only have my system at around 85 to MAYBE 95 dB on a continual basis. Anything louder than that is not typically good for your ears to have a system operating much louder than that. Most systems playing at that volume level are not using maximum output. Some speakers can handle large amounts or need large amounts of power to drive. Electrostatic, MBL, and other speakers might require or like large amounts of power, but in most cases, you'll probably not use much more than 20 or 50 watts, especially if you do things like bi-amping.
Don't judge a system by how loud it goes, since most of these places won't even turn up the system to maximum levels, because you can't sit within 60 feet of the speakers when they drive them to maximum spl. I have a pair of Meridian DSP5500s for mains, a DSP5000 center channel, with some other DevTech rears and a Talon sub and I can't sit in the same room after I turn up the volume knob past a certain point. Listening to a system in the 100+dB range is just not something good for your ears. When you go to a concert, break out your smartphone and a dB meter app and see what the dB is at your listening position.
Go to these sites and check out some of the most insane systems available.
HigherFi - Worlds Best HiFi High-End Speakers and Audio or
HIGH-END PALACE - The place for the world's best music systems!
And $50K for a pair of monoblocks isn't the high end, it's not more mid high end in terms of price. one can spend upwards of $500K for the Pivetta Opera or $200K for the Goldmund Telos 5000's, etc. so $50K for a pair of Pass is pretty cheap.
