I've had the II's and the 2.5i.
The II were veiled sounding by comparison to the 2.5i. They use a less accurate, more forgiving midbass driver than the 2.5i. The tweeter is a semi dome on the II and I quite liked its sound. The 2.5i has a metal dome tweeter that is more extended than the II's, but you're talking about the 2.5 speaker, which has the same tweeter as the NHT 1.3, which i've also owned. This tweeter is also more extended than the II's tweeter, but with the II's tweeter being more 'delicate' sounding, in a way (if that makes any sense).
As far as bass is concerned, the 2.5 and 2.5i have a single, inward firing 8" bass driver, in its own, ported enclosure(sealed off within the speaker from the upper drivers, from what i recall). The bass in the 2.5i is boomy, in my opinion, although does go down quite low and is certainly enough to circumvent the necessity of a subwoofer, in most cases, if driven with a suitable amp.
The II's bass drivers consist of two 6.5 inch drivers at the base of the speaker's front baffle, just off the floor. This provides a bass-coupling effect with the floor to assist in bass delivery. The II's are a closed design and are hence tighter in bass than the 2.5's, although they do not go as low in frequency.
Also, the II's cannot handle as much power or volume as the 2.5's can; my friends blew one of my midbass drivers on the II's when they were listening to music just a tad too loudly one evening (nowhere NEAR as loudly as the 2.5's could play with the same amps).
for 100 bucks, I would purchase the II's myself, provided the foam surround on the midrange driver is intact.
