Power Handling Capacity and Amp Output

You'll deafen yourself long before you blow the drivers, don't worry about it.

Yes, you would probably damage your headphones if used at that level for any extended period.

+1 to what tangster said. You'll use less than 1 mW to produce relatively loud levels with those headphones - 150mW would take your face off, and it wouldn't matter *what* happened to the drivers or headphones at that point (honestly you'd probably want to go to the hospital due to the pain, and you would have permanent hearing damage from the event as well). There is no "correct power output" for all headphones - by and large dedicated amplifiers provide many orders of magnitude more power than you will ever need, and there's nothing wrong with that (because it means the amplifier will very likely never approach clipping for normal use), as long as you don't put it up to 11 and blow your ears out.

I have an amp - putting out approximately 1.1 watts into my HE-500's. Would it be safe to turn the volume all the way up, since they are orthos? The lcd2 is rated for like 15 watts.

For the headphones or for you?

For the headphones, probably (but check with HiFiMan's specs first; I've yet to see a PM that has less than a few watts/ch max input though). For you, most definitely not.

I should add, this assumes a pretty much full-scale signal. If you do this with no signal input, or a signal that's 40-50-60 dB down, it shouldn't cause any trouble.

Want to use them as an alternative to desktop speakers :P

The funny thing is, that hifiman does not post any specs regarding max SPL and the like

They'll probably sound super tinny as speakers, just because they won't do a good job putting out low bass in a large space given their size. If you're really that desperate (where you can't buy "nice" speakers), I'd just truck down to whatever Denmark's equivalent of Wal-mart is, and get a cheapie pair of computer speakers and use those. Some of them come with small "subwoofers" and don't sound half bad (for the ~$30 they tend to cost) - would probably be more reliable and safe vs using your cans cranked all the way up.

I do have some bose 2.0 speakers. They are like 5-6 yrs old and they sound rubbish. Thinking about EQ'ing my HE-500's so that they can deliver better bass as 'speakers'. I don't dare to try anyway. These headphones are going to last decades 

Actually, they don't sound too bad if you use them as super-near-field speakers (1'-2'), and tilt the cups towards you. Of course, they won't give you the same "room filling" performance as even some crappy desktop speakers, and I doubt you'd get much of a bass boost even with EQ (no rumble, for instance).

 

Long story short, they'll sound x1000 better on your head! 

Soooo heavy. I'm getting neck fatigue after 3 hours 

Depending on the ohms of the headphone the amp can seriously distort when not even turned all the way up. Say a 16 ohm impedance headphone, your amp might only be able to deliver 50mW's (seriously I don't know how much ) without distorting.

There is probably more to it

 

As I understand it, generally the higher the impedance of a headphone, the higher voltage gain and output voltage an amp should provide, the lower the impedance, and especially for orthodynamic headphones the more current it needs.

 

Check out the article here for all the details..