Cabinet for Randall T2

Hi there!!! I am owner of a Randall T2 head and a Randall RA 4x12 XC cabinet. I tested this head several days ago in a guitar store and I was impressed by it's killer tone. So I gave away all my savings to have this head. The guys in the store gave me the cabinet that I mentioned above as an economic solution and as an ideal cabine for practising at home(!!!!!) and for live performances as well... Now the thing is, that so far I didn't accomplish to have a sound to leave me satisfied for my playing (heavy - thrash playing with a lot of screaming leads). Too much bass and "blur" in my sound. Is the cabine the problem? Shall I get an XL Randall which is ideal as it's said for a head amp like this or things are gonna be tha same again? Is the problem that I played this cambinet in a small room so far? If someone uses the same head and has a solution on this, please, enlighten me.... My guitar is a Razorback Dime (original, made in USA)
Thanks and sorry for my crapy English...