I was consider the following amps:
Echo audiofire 2
Will any of these drive the 880s or is there a better choice?
Single tube headphone amplifier, sold on eBay, I like the Indeed MK2 model.
Lots of Voltage for your 600-Ohm headphones
What are you using for a DAC?
The Indeed amp. is $76, plus $18 shipping.
The E7 is a DAC and amplifier, not something you would normally use with a separate amplifier.
The Xonar DX/D1 come with the CS4398 DAC chip, which is a fairly good DAC chip and the Xonar comes with Dolby Headphone surround sound for movies and gaming.
Unless you need something like the E7 for portablilty?
Dac Destroyer, USB-DAC. current bid is $38, add $9 for shipping.