Boss DR-55 Dr. Rhythm Modified. I'm the second owner of this drum machine and bought it here from the person who originally modified it. 
MODIFICATIONS: The modifications are in a secondary metal housing attached directly to the original unit. 
AC-ADAPTER: It is powered by a 6-volt AC adapter, which is included, and does not take batteries. The adapter plugs into the secondary housing.
INDIVIDUAL OUTPUTS FOR KICK AND SNARE: It can output all the sounds through a single cable, like an unmodified DR-55, but it also has individual outputs for the kick and snare, which can be seen near the Bass Drum Tone and Snare Tune knobs, leaving the hi hat in the main output.
Each knob works as follows:
Bass Drum Decay: This shortens or lengthens the kick/bass drum as well as thickens it and changes its texture. It can be lengthened to infinity. It can self-resonate even if the drum machine isn't playing a rhythm. It can get a good 808 tone.
Bass Drum Tone: This is a tone knob but also changes the texture and volume. At higher settings it noticeably makes the attack more aggressive and adds a slight amount of distortion.
Snare Drum Noise: This is a filter but also changes the decay and texture of the white noise.
Snare Tune: tunes the click of the snare, adding a noticeable tone at the higher setting, changes its texture and slightly lengthens its decay. 
Rim Shot Tune: adjusts decay and tone, pitch seems to be slightly affected at higher settings but that might be an illusion(?).

Combining these with the original tone, accent, tempo, and rhythm memory knobs gives a surprising amount of versatility.
I've never tested the foot switch, nor DBS and CSQ since I've never owned a footswitch nor a CSQ-100.