I also have a Krank Rev Jr., but mine is the 20W standard version. It does not sound very good at low volumes, IMO.
MAYBE if you swapped the tubes for some quieter 6V6's, and run it through a less efficient speaker like a Heritage Greenback, but the way it comes stock, NO WAY, IMO. I've used it with JJ 6V6's (not the least powerful 6V6's available, but quieter than the stock 5881/6L6's), and nope. Still have to run it pretty loud or else it sounds like a frying pan.