Yes it is very difficult but don't take the display of products too literally. We know it is unlikely you are going to find a local dealer with the speakers you are interested in mounted in a crossfire, and industry experts have been telling dealers for years to build realistic demo vehicles to address the average consumer, but thy find it better to create high dollar vehicles they can show off their custom skills (one of the reasons shops fail because if they got the job they can't charge enough to make up for; the loss of normal business generated from taking up space on the big project, the amount of labor time it takes to do it right, and deliver projects in a reasonable amount of time without pissing off the consumer).

However there are a few things to understand and things you can do within the space....for example

1. If you are listening to a pair of door speakers on a display board don't stand directly on axis (right in front of the speaker) try to replicate as best as possible the position you will face in the car. Off axis response is going to be a critical element for car speakers, in fact some brands design for it taking into direct and of axis reproduction

2. Power - try to find the closest representation of how you will be using them. Radio power = 12 watts per channel on a BTL amplifier no matter what the marketing is, more advance head units using digital dsp amps might get you to 20 watts @ 4 ohms. If you move to an off board external amp in the showroom and you get blown away with a 50x 4 amp without touching the head unit you know that the gains of the amp are set way to high. Regardless of the type of amp, power is power and doubling the power will only deliver a slight increase of volume change 3db. So going from 20watts to 40 watts of input nets you 3db, 40 to 80 nets you another 3db, 80 to 160 nets you another 3db, this gets you close to twice as loud at a 10db difference. You also begin to see why more is not always better because there are not many door speakers that are going to take 160 watts rms input. Also be wary of differences in amplifier brands. The hidden in plain sight trick that is used by manufacturers is to design the amplifier such that it does not take much to drive them. One company might use a fairly standard range of say 1v-2vrms while others will go .5v - 2v in the gain setup to make their amps seem more powerful but in reality they just reach max power sooner on the volume control and then distortion.

3. System - are you using an ipod/iphone or other device for a source? Use the same in the demo. If I play you a cut on a CD and you have the same cut at 128kbps AAC from iTunes I can bet the house my demo will yield a different level of performance than your cut...by a long shot! How good the system sounds starts with the content you put in....as the old saying goes....Garbage in Garbage out!

4. Lastly don't expect a 6.5" speaker to deliver earth shattering bass. Used properly most 6.5" drivers are good down to about 120hz before they tail off. Higher performance drivers down to 80hz before their output tails off. Generally speaking if you deploy a crossover between these drivers and a sub set at 12db slopes you should look for that 3db down point and double the frequency and dial that in...its a general rule of thumb. From there its up to the subwoofer system to fill in the bottom end.