The Logic Off Topic list

I'm trying to decide which pair of headphones to buy for now...

Part of the time I'll be listening to them while they are plugged
into an RME HDSP9632 (http://www.rme-
audio.de/english/hdsp/hdsp9632.htm )
which has a "Low impedance output (75 ohm) for headphones, stepless
output level through software faders"

The other part of the time I'm going to lug them to work and plug
them into an old SoundBlaster Live card in my workstation... No
idea what its impedance is but I'm sure it isn't pretty. I might
get a portable CD player but I'm sure most of them don't have
that great of sound quality either.. In any case I just want
something better than cheap $20 headphones to listen to music
with while at work, plus it will give me a chance to get to know
the headphones better.

I was thinking of getting some $200 Sennheiser HD580 headphones but
I'm afraid they would be too good as they have 300 ohms of
impedance. I glanced at some headphone amplifiers but nearly all
of them were designed to have multiple headphone outputs and all
I would really need is 1 high quality output... 

If I turned the volume up all the way on my computer at work, would
it still be too quiet to hear through the HD580s? I assume its
impedance is less than or equal to the HDSP9632's...

So does anyone know any models of headphone amps with just one
input and output that have a frequency response of 12-38k Hz like
the HD580 does, preferably with a THD of < .1% etc? I wonder
how much such a device would cost? 

Or do you think I should just get cheaper/other headphones for now?
I.e. maybe the AudioTechnica ATHM40fs which only has 60 ohms of
impedance? I just don't want to miss out on any bass. :-) Could
anyone suggest any other models I might want to look at, in the
retail-price-of-$270-but-really-sells-for-$200-range, that
doesn't have so much impedance so I wouldn't have to worry about
getting a headphone amp?

Thanks!
Jeremy