I did further testing and experimenting with EZD2 (in Cubase 7.5) with a virtual Instrument track and as a MIDI track.
Instrument track:
To use EZD2 you create an Instrument track and then select an 'instrument' - in this case EZD2. This opens an instance of EZD2 and adds a channel to the 'Input' section of the Mix Console. Using this fader I can change the level of EZD2. There is no fader in the 'output' section of the Mix Console.
If you open a second Instrument track to use with EZD2 then you must select an 'instrument' which opens a second instance of EZD2. There is another fader added to the 'input' section of the Mix Console. Each new instrument track opens another instance of EZD2 (or whatever other plugin you might be using).
MIDI track:
To use EZD2, I first add it as a VST 'Rack' instrument. Then create a MIDI track, select EZD2 from the list of instruments available in the 'VST Rack' and assign a MIDI channel for this particular MIDI track. This creates a fader in the 'input' section of the Mix Console and a fader in the 'output' section of the Mix Console. The fader in the 'input' section has no effect on the level of the MIDI being sent to EZD2. The fader in the 'output' section controls the audio return from EZD2.
Each instance of the Rack instruments can accept up to sixteen different MIDI streams (channels). When you open a second MIDI track to use with EZD2 (or another Rack instrument) you select EZD2 from the list of instruments available in the 'VST Rack' and assign a MIDI channel for this particular MIDI track. This creates another fader in the 'input' section of the Mix Console for the second MIDI track. There is still only one 'output' fader for EZD2 in the Mix Console since additional MIDI tracks use the existing instance of EZD2. Note that both of the EZD2 faders in the 'input' section of the Mix Console do not have any effect on the levels coming from EZD2.
Please note, in contrast to EZD2, for a 'MIDI track' assigned to other VST instruments the fader created in the 'input' section of the Mix Console does affect the level from the VST instrument.
More generally speaking, this is where the distinction between an 'Instrument track' and a 'MIDI track' is important (in Cubase). This second MIDI stream is sent to the same instance of EZD2 (or other VST instrument) as the first MIDI track. Therefore, one instance of the VST instrument can handle up to 16 different input MIDI streams. For an instrument like EZD2 this is not so significant since most people would not need more than one MIDI stream driving EZD2. For other VST instruments like Omnisphere or Halion, this is very significant since you can have up to 16 different patches (voices) from a single instance of the plugin.
For myself at least, the fact the individual faders in the 'input' section of the Mix Console control the level being sent to the VST instrument makes it easier to work on the mix using a single group of faders (the 'input' section faders). Because EZD2 does not recognize (honor) the input fader of a 'MIDI track', I find it cumbersome to have to think differently (and visually check a single fader in a different group) for the EZD2 (or SD2) plugin when mixing. This is not an earth shattering problem. However, it does divert focus from the mental overview of the mix.
Request / Suggestion:
When using a 'MIDI track' to access EZD2 (or SD2), please consider changing the behaviour of the fader in the 'input' section such that it will control the level of MIDI stream being sent to EZD2 (or SD2) as is the case for most other VST instruments.