Don't you have to change the bias of the amp if you change the tube from a 12ax7? Not sure how to do that. Perhaps staying with a 12ax7 is best but finding a better tube than the Sino is best in this case.
Not for little signal tubes, just power tubes
The response above is a bit misleading or, at least, incomplete and oversimplified.
There are several tubes that have the same pinout (the same pin goes to the same element in the tube: plate, grid, cathode in a triode tube) as the 12AX7 and use the same heater voltage.
Yes, you can interchange them without doing any harm. However, that does not mean that they are designed to use the same value resistors and other parts in the circuit. A circuit that is optimized for a 12AX7 and one that it optimized for, say, a 12AU7 are different. If you want to optimize the circuit for a different tube you do need to change the operating points including the bias (cathode resistor), the plate load (plate resistor), grid leak resistor, cathode bypass capacitor and maybe even the supply voltage and the negative feedback circuit.
The amplification factors of these tubes are much different. For 12AX7 it is 100. For 12AU7 it is only 20. The 12AT7 is 60. Another popular sub is the 5751, which is 70. They can all be used and they will alter the sound but they will not be operating as designed unless circuit changes are made.
I will be getting a pre amp to use and would that make a difference in regard to which is more important?
There are different types of preamps. Some provide gain (signal boost) and some not. Many times you don't really need any more gain but a preamp might be convenient if it has multiple inputs to connect multiple sources or even remote controls. If you use a turntable you will need a phono preamp.
Back in the old days preamps, or the preamp sections of integrated amps, had these knobs called tone controls. Very handy. If you wanted a bit more Bass you just turned the knob a little bit. Too bright? A slight turn of the a knob called Treble and it's fixed. No need buy several new tubes in the hopes that one of them would solve your problem.