It could go either way. I tend to prefer a modest amount of preamp gain, generally. Depending on the input impedence characteristics of your amplifier and the output impedence characteristics of the prospective preamp, as well as the quality and complimentary nature of the two, it is certainly possible that you would notice an improvement.
If the dealer is willing to make the sweeping claim that it will give an improvement then he should be willing to let you try the combination for yourself.
Absolutely try it if he offers a no strings audition.
If the dealer is willing to make the sweeping claim that it will give an improvement then he should be willing to let you try the combination for yourself.
Absolutely try it if he offers a no strings audition.