Well trying to get a Marshall 900 to sound like a VOX or a Fender is not going to work! I have a 900 50W combo, the Dual Reverb with EL34's and quite honestly I like the amp quite a bit...... for what I do it works. The gain is a little fizzy at times, but I use the clean channel more and I use a Marshall BB OD with it. Works for me.
You may have to look at Boutique to get both of those amps in one box. Or at least an amp that is EL84 powered, but that may lose the Fender vibe you want. Have you considered buying a Valvtronics?