If your wanting to spend 300, I would look into TUBE POWER.
The standard answer here is " Go to the store and play with all of them."
How much more sound do you want? I cant remember but does the cube have an external speaker jack? You could just pipe it into a 10 or 12 in speaker. That amp is designed for low level playing and pratice. If you want to play with a drummer,, Im thinkning at least a 15 to 30 watt amp. I held my own back ing the day with a little Marshall lead 12 amp.
A 5 watt tube amp = around 30 watts of solid state. If you have a multi effects, you really dont need a modeling amp, if its economy time,, look into Berhinger, or Bugera http://www.bugera-amps.com/EN/products/V5.aspx I have this one and a 65 Watt berhinger 2 channel (both the same company) Go play in the store and get what makes you feel good.
"Get that amp up to 13, if it don't feed back it ain't up loud enough." - Phill Williams
Mal - Well, lady, I must say, you're my kinda stupid.
Mal - Jayne, your mouth is talking. You might wanna look to that