If you're talking about the power section exclusively, you can vastly vary the feel and tone by the power tubes you put in and how you adjust your bias. 6550s will be harder and colder, 6V6s and EL34s can be rounder and more compressed.
A hotter bias will give you more compression, whereas if you bias it cold it will feel stiffer. Therefore, it is my opinion that the RM100 power amp doesn't have to be cold or stiff necessarily.
I think some of the sterile feel can come from the presence and depth circuit, unless it is fog lifted. The stock controls are not very usable in tuning the power amp.
So if you want to change the feel, you can always experiment with the power tubes and the bias, and consider an upgrade to the foglifter or even foglifter plus circuit. You may like the results!