Which headphones??

Thanks everyone! That was the second time beyer T70 came up. I'll look into those more, and also some HiFiMans, and sennheiser 600/650's.

Next question; how do you tell a headphones "sensitivity" rating? Lower ohm's more sensitive?

How do you tell a headphones "sensitivity" rating?

Sometimes it is explicitly specified, as sound pressure level (in db) for a 1 volt input.

In other cases it may be specified as SPL for an input of 1 mw (1 milliwatt, which is 0.001 watts). To convert that to voltage sensitivity use the equation

P = (Vsquared)/R

Where P is power, in watts.
V is voltage, in volts.
R is impedance, in ohms.

For example the T70 is spec'd at 250 ohms, 104 db/mw.

The voltage required to generate 104 db would be:

V = Square root of (0.001 x 250) = 0.5 volts.

To calculate the SPL that would be produced in response to a 1 volt input, so that you can compare to other phones which are spec'd based on a 1 volt input:

1 volt/0.5 volts = 2

db = 20 x (logarithm of the ratio of two voltages) = 20log2 = 6 db

104 + 6 = 110 db SPL for a 1 volt input

Best regards,
-- Al

Lol, so that's what it sounds like to my fiance when I talk to her about stereos or cars ;-)

Step up to the HD580/600 and you'll probably be much happier long-term, as they're much more sonically refined than the lower-tier Sennheiser models. You can pick up a used pair of HD580 (which I own now) for under $150 and the HD600 (which I used to own and should have kept: they're definitely a touch more transparent) for around or just above $200.

For context, I owned the HD555 modded to HD595 (model prior to the HD598), and the HD580/600 series is a huge step up. The lower models have a mid-bass bump and some grainy treble emphasis, but the 580/600 sounds smooth and neutral top to bottom (though some find them too warm).

Here's a great recent comparison of the HD580/600/650 series:

http://www.innerfidelity.com/content/very-important-sennheiser-hd-580-hd-600-and-hd-650

regardless of specifications and performance, headphones are way more individual sensitive than speakers.convenience, head size, shape, earshells it all matters to get a perfect headset. i get headaches and listening fatigue from overdefined HD580/HD600 bass. did not try hd650 as an example.
your best bet is either swapping them one after another by purchasing/selling or visit a good headphone shop or even audio festival to make up your decision.