auxinput,
As I recall the larger Walsh models are somewhat more efficient than the smaller ones, like the microwalsh, and overall they are not any harder to drive than most, perhaps easier. Not high efficiency like Klipsch though for example, for sure. OHM Walsh goes for extended bass in a smaller package so cannot be high efficiency.
Also, regarding coherency, I take that to mean clean integration of all frequencies for the listener. That is what OHM means when they talk about coherency with their Walsh CLS (Coherent Line Source) technology. Imaging and sound stage are different things. OHMS/omnis do those differently for sure, especially imaging. The imaging can be very focused when set up right or not so much otherwise.
Omnis and their ilk will probably never be as pin point focused as say a pair of very high quality monitors can be in practice.
The OHM Walshes go for a live like presentation in regards to sound stage and imaging, not a pinpoint one, which might occur in certain studio recording masters, but hardly ever live in real life or in live recordings.