I am the original owner of this Eastern Electric MiniMax DAC PLUS, serial number EE11080059.  It is in excellent condition +.

The ‘PLUS’ is noted for 3 things primarily:  1) Tube or solid state output, 2) Punching far above its weight class and 3) Allowing easy customization/tweaking via rolling output tube and/or op-amps.

The ‘PLUS’ is wonderful, but I moved to i2S from USB and from speakers to headphones years ago with combined DAC/HPA and Pink Faun i2S interface (PINK FAUN and Meister Jord cannot be recommended highly enough!!).  The ‘PLUS’ has been stored 7+ years (I blame this on an acute, since treated, case of the ‘Computer Audiophilia’ virus). 

The ‘PLUS’ is completely stock.  I removed the preamp tube and used the unit in solid state mode exclusively; in my system this sounded best. YRMV.  The stock tube (Shuguang 12AU7) is included.

I paid $1100.00 for the ‘PLUS’ in 2012.  I am selling the unit for $330.00 which includes shipping and PayPal fees.  You will not find this much flexibility and sound for this little money in any DAC IMHO. 

Highlights of the MiniMax Vacuum Tube DAC Plus:

• Sabre ES9018 DAC chips

• Separate Power Transformers for digital and analog sections

• Inputs : AES/EBU, BNC, RCA, OPTICAL and USB

• M2Tech OEM 24bit 192KHz Asynchronous USB input

• Tube and solid state output selectable

• Phase In/Out selectable

• Sampling rates: 16-32bit / 32KHz-192KHz

http://www.stereomojo.com/EASTERN ELECTRIC TUBE DAC PLUS REVIEW.html/EASTERNELECTRICTUBEDACPLUSREVIEW.html

http://www.dagogo.com/audio-blast-eastern-electric-tube-dac-plus-digital-to-analog-converter

http://www.digitalaudioreview.net/2010/12/eastern-electric-minimax-tube-dac/

http://www.enjoythemusic.com/magazine/equipment/1212/eastern_electric_minimax_dac_plus.htm

http://www.eeaudio.com/eeaudio_012.htm