As usual, the manufacturers dwell on amplifier power. We must stress that this feature is no guarantee of results either in sound quality or in the maximum volume you can reach. Volume depends both on amplifier power and speaker delivery and you are given no indication of how the speakers perform. So you should consider power as a general indication of the category the product falls into and remember that only the RMS power really counts. PMPO values in particular relate to nothing useful at all.
For the satellite speakers, most solutions are based on a wideband loudspeaker returning frequencies at around 150Hz to 20kHz. This works well if the speaker is of good quality and has the right features. In theory, the smaller ones reproduce the high range better but find it harder to match up properly with the subwoofer and get the right midrange and low-midrange frequencies. So you have to find the best compromise here.
Another solution is a two-way speaker with a midrange and a tweeter. This is the premium but a good wideband is better than a poor-quality two-way speaker. Then there is the trendy micro-drive formula with a set of tiny speakers working together to produce adequate midrange sound. The main advantage here is looks as these satellites can be very slim. Some systems equipped like this offer good results, but not all. In general, micro-drives do not reproduce midrange sound properly and have trouble matching up with the subwoofer. Some of them can't even reproduce high range sound.
We must be realistic about the subwoofer, the kingpin of the system with the power supply and electronics. Everyone would like it to be compact, lightweight and powerful. But you can't have it all ways, at least not with the technologies conventionally used. A good subwoofer, able to restore the entire bass range and not just a part of it, has to be pretty bulky because, to reach this level, the loudspeaker must be wide. It needs a diameter of at least 15cm if you want the best results. Less than this and some bass range is lost. The acoustic load used of course affects performance, but don't let yourself be overwhelmed by what the manufacturers say about this. It is very hard for a non-specialist to evaluate these techniques, so just trust your ears when you try one out.
We can only advise you to look at the way the controls are designed and operated: the best system is the wired remote - except for the infrared remote, but you only get that on a few high-end models. Controls on the subwoofer - worst of all, at the back of it - are not convenient and satellite controls do not suit this part of the equipment, which is mostly set at some distance.