I can think of a few situations where such a device might be useful.
1.If the output stage of a component (in your case preamp) is incapable of driving a specific load (your amp).In my case I use a Zman Audio Signal Enhancer (a small inexpensive single-ended tube buffer stage) between Sony tv and VTL preamp.
2.If you have a noise problem,such as emi,rfi,or any cable induced hum.
3.If there is an impedance mismatch between source and load.
Those are really the only three instances I can think of where buffer stage or balanced conversion would be needed.Don't know how it would increase dynamics by 20 or 30 percent UNLESS one of the three conditions mentioned above applied to your situation.One thing I can say for sure is that adding an un-needed component in the signal chain WILL introduce additional coloration into your system.The additonal coloration might make your system sound better or worse to your ears,no way to tell without trying it.Let us know how it turns out.
Best Regards,
Andy