OK so I found a very decently priced amplifier that works well with my setup. It's called the Sense G5 hybrid amplifier. It really helps to roll off the treble that most complain about. I got it for ~$150 from this seller:
"12AU7 tube + VMOS transistor class A output
Power output: >1000mW
Frequency response: 10Hz-50KHz
Headphone impedance: 32Ω-600Ω
Signal-to-Noise ratio: >90dB
Line input: RCA
Headphone output: 6.35 mm stereo jack
ALPS volume control
WIMA MKP10 ELNA AV BC capacitors
Dimensions: 163 x 252 x 68 mm
Weight: 2.5 Kg
Input voltage: AC110V-120V 220V-240V 60/50Hz (110V version will be takes 5-10 working days to order)"
It took over a week to get it to me with EMS shipping. It sounds better with the Hot Audio Dac Extasy than the F17, E09K, and O2. The only problem I'm having is that after about an hour I hear this constant high pitched whine sound come through the headphones, even when the volume is turned all the way down. (Ground Loop maybe?). So after I turn off the unit, take out the tubes and wait 30 minutes or so and put the tubes back in. Annoying sound disappears.