So I've spent some time slowly bringing everything online, did the tests last night then made up some RCA to XLR cables to get a signal into the thing:

My pre-amp is going to look like an amphenol groupie

Used my disposable speakers and an ipod, all good
Then connected up the Mars-pre with the ipod, all awesome! No bangs anymore at on/off, just slowly gets louder/softer. Still a big bang when switching to phono as the tubes get up to voltage, no speaker protection triggered so will have to watch that.
Then got it installed in it's home:

The word you're looking for is "headroom"... Lol, who am I kidding, the word is "overkill"
Quick listening impressions, very clean and precise, definitely more studio than hi-fi, which is perfect for me. There's also the feeling in the background that if you let loose it would throw the speakers across the room just for fun.