You might even get away with just one comparison page on your site.

On that page, pick one song and demo it as many ways as you want (sound card, basic soft synth, superior soft synth, then one or more of your hardware synths.

Write a blurb about how the quality comes from the sound source, as these samples demonstrate.

Then anywhere else on your site where you think a comparison might be needed, just add a link to that page.