Hello everyone, 
 
I'm new to Head-Fi and have spent about a week browsing the fora. My apologies if this issue has been covered elsewhere; I've combed through posts relating to each piece of equipment and thought I might as well ask a specific question: 
 
I'm intending to buy a set of the Sennheiser HD 650s.  Auditioned a pair along with some Grado 325i's and PS 500's, and they drew me in like I never expected.  I have some Grado SR60s that I got about a decade ago, now leaving black foam dandruff all over my shoulders, but I still love them.  So I expected to love the higher-end Grados and was surprised by how absorbing I found the Senns.  Totally involving, trance-like, toe-tapping, to the same track, over and over (some Diana Krall cut with piano; 4th track I think on the best of CD).  
 
Bearing in mind some good advice I read online over at Hedfonia (better to own three $300 headphones than one $900 headphone) I've decided to go for a different sound and get a pair of the HD-650s, and I don't think I'm going to be sorry!    
 
However, I also want a good DAC to drive them and play through my iMac (2010) (lossless files, etc.). I'm going to use the DAC for the headphones, but they will also be powering my Aktimate Micros (love those; built-in USB DAC but 16bit/48khz).  I can't decide between: 
 
1. Audioengine D1: great price and portability; very well-reivewed in these fora; I'm worried they won't have the power to bring the 650s to their best. 
 
2. Cambridge Audio Dac Magic Plus: great connectivity.  I auditioned the headphones through these at the store; liked them.  I'm getting an ever so-slightly mixed vibe from what I'm reading around in Head-Fi.   
 
3. CEntrance DACmini.  For some reason I'm tending in this direction. Great reviews, clean sound, relatively little coloration.  Probably with the variable upgrade. I like the fact that the president of the company is regularly posting and answering very specific questions on these fora!    
 
This is my first system, and I'm ready to get something nice but I don't want to spend a ton.  I don't imagine upgrading for a while -- want it to last and make me happy.  
 
Any thoughts appreciated (including friendly direction to posts where this has already been covered).  
 
deepwoof  

You did not specify a budget but from the looks of it it seems to be under $600 for both dac and amp.  I have not heard all on your list but have heard the Centrance and feel it woould do well.  Since it is for an imac perhaps a good tube amp like the La Figaro 336 C and a good dac entry level dac like the Devilsound.
 
A big factor in ultimate SQ from your mac is going to be what player, what quality of files, OS and tweaks you can do to get the mac to sound its best. 
 
Good luck with your quest.  The Senns are really nice and mate well with many amps.

If you can stomach the price the Centrance DACmini would be the one to go with. Nice styling which goes well with Apple computers, supports 192kHz sample rates and 96kHz over USB. 
 
For the same price you can go all solid state with Schiit. That gets you a Bifrost DAC with USB option, and an Asgard solid state Amp. Add $20 for cables and you have a nice stack made 100% in the US. Schiit is a really great company too.