Hi, I have just purchased one of these amps built by Nik.
Just wondering if anybody can help me.
I really bought this model for the overdriven sound as I already
have a Silverface Deluxe Reverb which has beautiful cleans.
I can't seem to get a decent overdriven sound.
The upper register is good but the bottom end
particularly the E string sounds really loose and farty.
I'm using an Eminence Cannabis Rex 1 x 12.
Is this something inherent in OTS amplifiers? The tubes have burnt
for about 10 hours. Will this settle down with time?
Any help or advice would be gratefully received.

I've had mine for about 2.5 weeks with I'd guess about 30 hours on it.  I think the overdrive sounds are fantastic... i boxed up my Zendrive the first night.  A couple thoughts...  run the overdrive (red) with the preamp boost (green) on as well.  I have found that to be plenty beefy.  Play around with the Ratio and Level controls to find more of what you're looking for. (I haven't touched it yet but there's an OD trim knob oon the back panel to adjust as well.)  I'm running through an Eminence Neodymium that has been reconed with a Tone Tubby hempcone...  sounds fine... I think your C rex would be in the same ballpark.  I also have an EV 12L, but that's a bit bright for me right now... at least in the small room where I play. 

There are so many variables and knobs to tweak... it takes time and experimentation... but I'm loving the sounds I'm getting.  I have been playing a tele through it most of the time... but my lap steel with humbuckers sounds fantastic as well.  I've heard that it takes about 60 hours of playing time for the amp to get "burned in" so hang in there.  Hope you find the sounds you're looking for!