By now some of the reasons why speakers can sound so much different is becoming apparent. If you gaze upon a speaker's frequency response curve, you'll notice that most of them have 4-6dB of variance across common frequencies (hence the use of the +-3dB spec). This level of variance generally overwhelms the difference from the electronics.
Two speakers that both measure at +-3dB from 35-18Khz, can sound dramatically different. One may be up +3dB across the 60-100Hz range and -3dB from 8Khz-12Khz. If the other is the opposite, then the resultant sound will be very, very different.
Most of the adjectives being discussed here are related to frequency response - "warm" speakers can generally be identified by their response curve, likewise for "laidback" and generally "forward" speakers.
Dynamics and soundstage can be different stories though. While it is true that very efficient speakers will also usually have good dynamics, it is hard to predict which medium efficiency speakers will excel at dynamics, this can be dependent upon which amp is used to drive them. For example, I've found that while Magneplanar speakers can have euphonic attributes when driven by low-to-medium powered tube amps, that to get the best out of them on dynamics and resolution requires a high-current amp (and usually a solidstate amp). Of course, one might still better like their Maggie with a tube amp and that's their choice.
Soundstage can be affected by several factors, including the cabinet design. For example the now-defunct Spica speakers used inexpensive, common drivers, yet threw up wonderful soundstages due to the cabinet designs employed by John Bau. Bau used precise driver matching, sloped & damped baffles, and time-aligned driver mounting to achieve these results. While John Dunlavy's designs also produced excellent soundstaging and used precise driver matching, he went with tall, multi-driver arrays and custom-designed first-order crossovers to achieve it.
If one is really going to get into critical listening and optimizing their audio system to meet their preferences, I know of no way of doing this without listening to a lot of music and equipment. This process can be simplified by getting familiar with the terms being bandied about here, listening to discs like the Chesky demo disc, and at least listening to a few different systems. Listen to the Chesky a number of times in your system, then take it with you to audition other systems. This will help you to more quickly notice differences and could even become fun to do!
Along the way, spend some time in discovering your own preferences. Don't adopt what others consider to be the "best" sound. There are a thousand "best" types of sound. Most of all, don't let yourself be pushed into accepting what someone defines as the "most accurate" sound as the sound you want to achieve in your listening room. It's all about what gets your juices flowing.
Tom B.