I just really can't offer meaningful comments on the P3s vs. larger Harbeths.
What I can say is that these little speakers did truly amaze me. They sound 'big', at least in a mid-sized room, and astonishingly there's hardly a need for a subwoofer. You don't feel like any bass is missing. Apparently they are down only 10 dB at 30 Hz due to the sealed alignment. And, as much as I hate to admit, the sealed enclosure gives a cleanliness to the bass that is only bettered by open-baffle. The best ported enclosures will reveal at least a bit of overhang to the bass at times.
What I can say is that these little speakers did truly amaze me. They sound 'big', at least in a mid-sized room, and astonishingly there's hardly a need for a subwoofer. You don't feel like any bass is missing. Apparently they are down only 10 dB at 30 Hz due to the sealed alignment. And, as much as I hate to admit, the sealed enclosure gives a cleanliness to the bass that is only bettered by open-baffle. The best ported enclosures will reveal at least a bit of overhang to the bass at times.