Hmm, my first thought was "are you using fresh beans, ground on demand, and tamping properly?" but you seem to have those covered!
I havent used this machine but I can guarantee that its capable of producing great espresso (with great crema) simply based on the fact that lots of CSers own them, and lots of sponsors sell them.
Is your machine clean? Does it get a chemical backflush a few times a month?
Do you flush before each shot? If youre not, this could be burning the coffee and killing the crema. Just flush a little water through the grouphead before each shot (to get rid of the super-heated water from the HX) until it stops spitting.
Is it running hot? To answer this, when youve left the machine for 10 minutes or so and then flush water through the group head, how long do you need to do so before it stops spitting? If you need to flush more than, say, 100mL (others might have a better estimate there...) then your machine could be set to too high a temperature.
How do your shots taste? How do they look when they are extracting? If they taste burnt, or bitter, or sour, or thin and watery... or if they are gushing, blonding early, or running very thin - this could give us some idea of whats wrong.
Have you tried different sources of fresh beans? Some may produce more crema on your machine than others.
Hope something of that is helpful.