[plexxx]

 
My current setup is playback from an ipod connected to a Pioneer AV receiver that has a proprietary ipod line-in connection.  I am using a Musical Fidelity V-CAN amplifier connected to the tape-out connection of the Pioneer and have Beyer DT-990 headphones connected to the VCAN. 
 
I am very happy with the Beyers sound and wondering what investments I could make to improve it further.  A dedicated DAC feeding the V-CAN?  Change to a source that can play FLAC files?  Take the receiver out of the equation or leave it in?  All of my music is on a NAS so I would consider a squeezebox to stream media.

 

[NA Blur]

Personally I run uncompressed audio through my m903 both DAC and Amp into my DT990 ( 250 Ohm ).  This combo is really amazing.  The m903 drives the DT990 so well and after testing the DT990's with many amps I know that they scale well with better equipment.
 
Having not heard the V-Can amp it is going to be hard to suggest improvements, but I think an Ultra Desktop Amp or m903 would certainly do the job.  The Music Hall 25.3 USB DAC and head amp is also a musical amp that I like.  The Headroom Micro runs $350 and would be an improvement over your V-Can, but it does not have a DAC so would you have to continue using the DAC on your Pioneer or find another DAC.
 
Perhaps even the CENtance DACport would work really well for you.  The DAC is really quite nice and it can drive your DT990's just fine if they are 250 Ohms or less.  It runs $400.