Focusrite posted this information regarding the headphones they used for designing the VRM Box...
"Which headphones was VRM designed to work with?
We used the Sennheiser HD 280/HD 650, Beyerdynamic DT 100, Beyerdynamic 770 and the PROline 650s to test VRM with, though during development the concept was tested on a wide variety of headphones of different designs (e.g. open and closed) and of varying cost and quality.
Obviously the better the headphones in terms of frequency response, the more the individual speaker's qualities will be discernible. However, the VRM system was not designed with one specific model of headphones in mind.
When considering headphone impedance, the general principle is that higher impedance headphones typically have a flatter frequency response, however they require more power from the headphone amplifier to provide the same output level as headphones with a lower impedance. Having said this, the VRM Box's headphone amplifier should be powerful enough to drive higher impedance headphones at a high enough level for most purposes."
I've seen where Focusrite has supplied VRM Boxes out to reviewers along with KRK 8400 or 6400 headphones (both 36 ohm) so they obviously feel those are a good match too.
Now here are my initial thoughts after briefly using it for about a week...
I'm still evaluating my VRM box but my initial feelings are positive for those who are interested in the device. I found my Sony MDR 7506's (63 ohm) to be a good match with the device.
I also tried high impedance versions of AKG K240, Beyer DT100 and an old set of Sennheiser 424's and found the VRM box doesn't really drive these hard enough for mix evaluation applications.
I wouldn't consider using the VRM box to replace my actual near-field monitors but it is fine as a stand alone headphone amp for times when I can't run speakers. I do believe that it will serve well as a supplement to help with mix compatibility/translation for trying out mixes on different virtual systems. Now I've found myself using it as a basic headphone amp bypassing its speaker/room emulations for general headphone listening. I do, however, plan to use it regularly as a final step to assist with mix translation after first creating a mix on my trusty near-field monitors. I used to own a set of Yamaha NS-10M's and hated them, the VRM Box does give an accurate representation of how I remember them sounding. I can't personally compare the accuracy of the other speaker models since I've never used them but several manufactures do endorse the emulations by lending the use of their name with the speakers.
Paging bdasilva!!! Since you are using one of these too, would you share your thoughts on the VRM Box for anyone else considering them especially since you are using this with Sennheiser HD280's.