OK - so HE thinks they are capable of more, so sounds like he thinks you could have better front-end equipment to drive them .....
DO YOU like the basic sound?
If so, then either ignore him, or if you're up for seeing what more they can do, take them to his (or another) shop or get some home dems to see if he's right!!
MOST speakers are capable of more than we get from them, as most speakers don't have £50k+ worth of kit driving them - BUT it's all a case of how much is worth spending on more CD/AMP etc before the speaker starts being the limiting factor......
Do you have a budget in mind of what you would spend to make it worthwhile for you??