Having worked in a 'high end' audio store in the mid-90s, I have heard a wide range of speakers from that time period, including both that you've mentioned. Not that my opinion should REALLY mean anything to you, but here's what I think:
Mirage M1si - Need LOTS of room for optimal sound reproduction. Bass goes very, very low, but can sound a bit bloated depending on the room setup and amplifiers. The speaker are detailed, but certainly not hyper-detailed as some are these days. I found, for the most part, that their midrange could have been more forward (a bit of midrange suckout), but that could simply have been the electronics or the room setup (as I was just a small-fry in that store, I didn't have much say in what was hooked up to what in the 'high end' room). The bipolar design provides the listener with a wide soundfield, but perhaps not as accurate pinpointing as a pointsource speaker.
NHT 3.3's: In my opinion, a much more accurate speaker. Clinical, some would say, but I can tell you that when you shut your eyes, you won't believe how amazing the sound can be with these beautiful slabs of speaker. One major caveat: MUST BE PARTNERED WITH HIGH QUALITY, SMOOTH SOUNDING AMPLIFIER(S), or the sound will just be too harsh for longer listening periods. These speakers are meant to be placed up against a back wall, so it's my opinion that they may be a bit less intrusive than the M1's. Bass goes low...VERY low and, from what I recall, is tighter than the M1's. Detail retrieval is top notch and, because of their narrow front baffle, they image like champs. Some would say that they are unforgiving of poor recordings, but it's my opinion that they reveal the music for all its good and bad (which, to me, only adds to the presetation). They play nicely at lower volumes, but can really, REALLY knock your pants off if you want to turn them up (again, you HAVE to have high quality, high amperage amplification).
In case you hadn't already noticed, my nod goes to the NHT's. If I had the space (and the money), I would likely pick up a pair as I've been a longtime fan of 3.3's. Sure, in this day and age, I'm positive that there are better speakers out there, but I seriously doubt they can be bettered for the money for which they are sold now.
Again, I reiterate that I am in the 'accuracy' camp rather than the 'forgiving' camp and because everyone has their own tastes, many people might completely disagree with my comments.
Mirage M1si - Need LOTS of room for optimal sound reproduction. Bass goes very, very low, but can sound a bit bloated depending on the room setup and amplifiers. The speaker are detailed, but certainly not hyper-detailed as some are these days. I found, for the most part, that their midrange could have been more forward (a bit of midrange suckout), but that could simply have been the electronics or the room setup (as I was just a small-fry in that store, I didn't have much say in what was hooked up to what in the 'high end' room). The bipolar design provides the listener with a wide soundfield, but perhaps not as accurate pinpointing as a pointsource speaker.
NHT 3.3's: In my opinion, a much more accurate speaker. Clinical, some would say, but I can tell you that when you shut your eyes, you won't believe how amazing the sound can be with these beautiful slabs of speaker. One major caveat: MUST BE PARTNERED WITH HIGH QUALITY, SMOOTH SOUNDING AMPLIFIER(S), or the sound will just be too harsh for longer listening periods. These speakers are meant to be placed up against a back wall, so it's my opinion that they may be a bit less intrusive than the M1's. Bass goes low...VERY low and, from what I recall, is tighter than the M1's. Detail retrieval is top notch and, because of their narrow front baffle, they image like champs. Some would say that they are unforgiving of poor recordings, but it's my opinion that they reveal the music for all its good and bad (which, to me, only adds to the presetation). They play nicely at lower volumes, but can really, REALLY knock your pants off if you want to turn them up (again, you HAVE to have high quality, high amperage amplification).
In case you hadn't already noticed, my nod goes to the NHT's. If I had the space (and the money), I would likely pick up a pair as I've been a longtime fan of 3.3's. Sure, in this day and age, I'm positive that there are better speakers out there, but I seriously doubt they can be bettered for the money for which they are sold now.
Again, I reiterate that I am in the 'accuracy' camp rather than the 'forgiving' camp and because everyone has their own tastes, many people might completely disagree with my comments.