IMO, it's likely that a difference in sound is going to be attributable more to the preamp/amp impedance match than by the use of XLR>RCA adapters to run single ended out of the preamp to the balanced inputs of your amp, especially if you're mixing a tube component with a solid state component.
Another unknown is if your preamp and/or amplifier are a differential balanced design, or if they simply have XLR outputs and inputs...perhaps transformer coupled, but not truly balanced operation.
One thing is for certain. If your amplifier is differential balanced, you will give up the noise canceling benefits of balanced operation by feeding it a single ended signal.
Without knowing the components, it's hard to say what is applicable to your situation.
Another unknown is if your preamp and/or amplifier are a differential balanced design, or if they simply have XLR outputs and inputs...perhaps transformer coupled, but not truly balanced operation.
One thing is for certain. If your amplifier is differential balanced, you will give up the noise canceling benefits of balanced operation by feeding it a single ended signal.
Without knowing the components, it's hard to say what is applicable to your situation.