The Maggies at least, will have no real cabinet resonances, unlike most other speakers(which have enclosed backs) seem to suffer from(this coloration can be avoided with enclosed systems, but it tends to be very costly to avoid, and as a result, usually ends up being a feature of only very expensive closed systems). Of course, they can still have resonances inherent of the drivers, while having no substantial enclosure resonance. The speakers require substantial space, as you refer to it, probably because (1) you require at least a 5-6 msec direct vs. rear reflection delay(this means spacing the speaker a minimum of 3' from the rear wall, ideally about 4'-4.5'). In addition, while I have not seen the off axis response of the particular model to which you refer, I expect it to be dismal. This means that if you place it far from a side wall, and relative close in proportion to listening position, that the non-matching off axis response will be heard to a lesser extent(poor off axis response does not typically result in positive results when allowed to contribute substantially). You can render this a non issue and place the speakers close to side walls by using large broad band absorption panels at the 1st side reflection points. In any case, substantial room treatments are really needed with speakers that have poor off axis response, as credible perceptual research has demonstrated time and time again. If you add a subwoofer, be certain to use an active filter on both the main speakers(to cutoff LF) and the subwoofer unit. Some recievers have adequate control and type of crossovers built in. But better results are usually had with external processing(usually only possible if you are using seperate amplifier/pre-amp units where you can get access to the line signal between devices).
-Chris