Vox Tonelab modeler - tube change?

[futbol1097]

After some research I have decided to go with a Vox Tonelab amp modeler for home recording (sorry Pod fans). The tube used in the modeler's circuitry as a power amp tube is a very cheap "12AX7/ECC83 dual triode vacuum tube." While the tube does apparently work, contrary to some feedback that it's just for show (an LED behind the tube lights it up to give the impression that its just like a real tube amp), I was wondering if changing out the stock tube with something else would improve the sound. I'm not sure how much the tube figures into the modeler's sound to begin with so was hoping to get some Tonelab users to weigh in on this. Could you potentially get a better sound from this modeler with a tube change? What tube would be recommended for this?

Thanks for the help