If you are a DIYer OR if you hire someone like
http://www.taylorspeakers.com/ or
http://salksound.com/about%20the%20custom%20alaternative.htm
you can clone Gary Dahl's hybrid horn speakers. The J2 should have no trouble driving the Azurahorn 425/Radian Research 745NeoBe driver combo and GPA's Altec 416-8B alnico midwoofers.
http://www.azurahorn.com/azurahorn_horns.html
http://www.usspeaker.com/radian%20745neoBepb-1.htm
http://www.greatplainsaudio.com/downloads/416-8B%20Spec%20Sheet.pdf
Gary demoed his system at a local Seattle audio club last month
http://www.diyaudio.com/forums/multi-way/100392-beyond-ariel-1356.html to a quite enthused and pleased audience.
Those mono blocks are Gary's clones of Lynn Olson's Amity amps http://www.nutshellhifi.com/triode1.html I think they are 25 wpc into 8 ohms. If so, then the J2 should have no problems driving everything above the subs.
The passive two way crossover use Dave Slagle's
autoformers, rather than resistive pots to balance levels between the horns and the Altecs
http://www.intactaudio.com/atten.html
Gary's subs are 15" Acoustic Elegance drivers with passive radiators, driven by Class AB plate amps. Or you might want to have Jim Salk build you a pair of his own versions of Brian Ding's 12" sealed servo subs
http://salksound.com/salkrythmik%20-%20home.htm
Here's Gary's report on his final system tweaks (save for those on the RAA: Lazy ribbon tweeters, which his still wringing out the last bit of coloration. Finally, here’s Gary recent summary of the last of his basic system tweaks, and where he becomes more pleased than he ever thought possible with the sound
http://www.diyaudio.com/forums/multi-way/100392-beyond-ariel-1295.html.
So if you want to play rock music with a low power amp like the J2-and if you work with builders like Lee or Jim and Martin and Dave and GPA's Bill Hanuschak, I'd think about cloning Gary Dahl's speakers, or at least his mains.
Good luck!