I've used an ISO cab and AXE FX 2 live (and briefly owned a Torpedo LIVE) and can share my thoughts and opinions. This is all based on my experience.
1. Used a RIVERA Silent Sister ISO live twice. At home and at practice, it sounded great: didn't sound boxy, and was able to EQ it so it can sit in the mix nicely. Live, I really couldn't tell because we're at the mercy of the sounguy (we're an original hard rock band w/o own soundguy). So the only "feedback" (no pun intended) I can give is what I heard onstage, which we all know it's never a good way to judge what the audience is hearing through the FOH. With that said, the first gig my tone was blaring through the house monitors (I told the soundguy that since I don't have a backline I needed to hear myself through the monitors). The second gig, I decided not to say anything to the soundguy and have him mix my monitors normally. Well, I couldn't hear myself at all! Bottom line with my experience using an ISO: it can work, but for me, it's too much gear to lug around because I would need my own monitoring system (wedge, small 112 cab, etc).
2. Torpedo LIVE. I had one for about a week. It sounded really good, but only listened to it through my home's studio monitors and headphones; never got the chance to try it a gig volume (rehearsal or live). After I placed it in my rig, there was this massive ground noise that I couldn't for the life of me get rid off. Looking back, I'm sure it was user error and not the Torpedo, but I got so frustrated with everything I decided to finally get an Axe and get rid of my tube amp and rig!
3. Axe FX 2. My other guitarist has been using one for about six months so I had some "experience" already. At first he was using it with a poweramp (Matrix GT800) through a 212 cab (Orange) and mic'ed so it was still more traditional than how many are using it today (including us, see below). Also, at that time he was on v6 or 7 I believe. Anyway, I was able to sell off some gear and get a hold of a used one. Tried it at home first, had a "meh" kind of feeling and at this point was really, really frustrated (note: for those wondering why not just use a 412 with amp, I'll explain in a bit). So I began tweaking, and tweaking, which I was afraid of after reading online the reason many stay away from this unit (and I'm not a tweaker). Another gig was coming up in a week and decided to just use it. I decided to go direct FOH and use a FRFR for my own monitoring. As for my own "monitoring" I only had a Mackie wedge (which we used as part of our PA system at our rehearsal studio). Not the best choice, but it was something. Well, the gig went pretty well. I was able to hear myself, adjust the volume onstage and not affect the FOH and soundguy. The tone I was not crazy about. Had a few more gigs, and tweaking in-between. One show I decided to leave my wedge and just "rely" on the soundguy to mix me through their wedge and I was so loud that there was feedback all over the place (but not through the FOH). Still, it was a difficult show. During this time I'm selling gear to get enough to purchase a high quality FRFR (was looking at the RCF since the CLR were not available yet). Then, v10 came out. That, to me, changed everything! Again, this is my own opinion. I felt that I was able to dial in a good sounding tone and EQ it to sit nicely in the mix. The other "revelation": I got myself a set of IEM monitors. My AXE Out 1 is going to the FOH and the Out 2 is going to my IEM. Also, I have an ambient mic near me that acts as my "ears" and I'm set! I can hear everything! And I don't have to bother anyone: the soundguy can mix me however he wants (I now tell him not to put me too loud in the monitor or just very little). Had four shows so far with them and I'm loving it! Also, my other guitarist now goes direct to FOH and is planning on getting his own IEM too. The singer is on IEM and the drummer too (headphones). Bass player is still "old school" but might come around eventually
4. Kemper. Never had a chance to use them but from what I've read and the videos I saw it sounds like a very good unit. For me, the AXE was a better fit.
I've been using a tube amp and 412 cab all my life onstage. Some nights it sounds amazing, others not so much. The thing about tube amps and cabs onstage (for me and my experience and my band situation) was that I just could never crank it up to get to that sweep spot (with the 5150), or sometimes I would reach that sweep spot with an amp with good MV (Dual Rectifier and FUCHS Mantis), but could not hear myself onstage cause either the drums are too loud, my monitors are too loud, or something else. Also, the cabs are sometimes mic'ed well, and no matter how "great" your amp sounds onstage, it sounds like sh*t to the audience 'cause the mic is not placed right, or it got bumped (which happened on more than a few occasions). I just came to a point in my playing that I wanted consistency, less volume on stage, and a good sounding "mic" tone mixed with the rest of the band.
Hope this helps!
PJ
PS: Next week we're sharing the stage with RED and the sound system there is amazing! In four weeks we're playing at Irving Plaza in NYC and the sound is also amazing. Last month we shared the stage with Nonpoint and Hinder and afterwards the soundguy came to us and said how good and clear we sounded and he had a good time mixing us. It's funny that Nonpoint were using FUCHS amps 'cause before going with the AXE I had an endorsement deal with FUCHS and was playing a Mantis (before that it was a MESA Dual Rectifier and Peavey 5150). Amazing amp, still miss it, but for my situation now, I'm happier with the Axe. Nonpoint's sound was amazing (all mic'ed 412 FUCHS cabs), but again, own soundguys and own monitoring engineers.
