but I would think the 2.6 would have a noticable increase in authority to it bass.
It does, below 50 Hz. Flat is flat, I don't think you're going to notice any difference in the authority of the bass above 60 Hz or so. In fact if you look around there are people that prefer the sound of the passives over the actives (
http://www.hometheaterforum.com/htf/speakers-subwoofers/152832-infinity-intermezzo-2-6-a.html ). I don't, I think they're too close to call and there might have been other factors that influences those peoples impressions, but...
The other thing that's nice about the 2.6 is that you can get by without a sub if you dont want one or cant afford one.
You're certainly slightly more able to get by without a sub (which is one of the reasons I specifically recommend the 2.6 to people that can't or won't go with a sub) but of course
really you still need one. Going permanently subless (or maybe if you're planning on powering them with a tube amp or something else that is very low power) is really the only time I'd recommend the 2.6 over the 2.6p. Otherwise I think the value of the powered woofer is almost entirely eliminated by having a subwoofer and the fact that you don't have to deal with old Infinity electronics, don't have to worry about power cords if you end up using them for surrounds (which is what I use mine for), and the fact that they're cheaper, handily tips the scale in the 2.6ps favor.
Sorry for your trouble with the amp. I've read a few of your posts and I seem to remember you picking up the 1.2S. Great sub. Hopefully you were able to get it fixed without much hassle.
The 1.2s has actually been fine, it was the amp for one of the powered woofers in the 4.1ts that's given me problems. Twice. Although the second time it was because it wasn't repaired correctly the first time. And now the amp in the 3.5c is being wonky. Whenever there's a power outage it wont turn back on unless I just leave it plugged in and powered off for 3 days or so. I'll get it fixed sooner or later (hopefully), probably when I live in the lower 48 and won't have to pay 200+ for two way shipping. But it is annoying. It's off right now in fact due to a power outage a week ago. Every time it happens I think maybe this time it wont ever power on again, we'll see.
I think potential problems requiring not too expensive fixes (sub repair was ~170 or so IIRC) is not a bad price of admission for the 4.1ts (and the 3.5c) because they're very impressive speakers. But with the 2.6 you have the option to eliminate the those potential problems, and since the advantages of the 2.6 over the 2.6p are IMO minimal (or potentially non-existent), I'd go the other way.
Either way though, you're getting an amazing sounding speaker for a bargain basement price. I bought my 2.6ps at the same time as my 4.1ts but the 2.6ps showed up first and when I hooked them up and compared them to the B&W 602 S3s that they were replacing I was very, very impressed.
Just my two cents

. (okay, more like $1.25)