To maximize you're existing mixer, you would want (4) passive/unpowered speakers, two for mains, two for monitors. Lot of good choices out there. Call Mike at Audiopyle (firstname.lastname@example.org
, 707-315-6204 ) about RCF ART 3 series. Compact, lightweight, inexpensive, blows away most competitors. FBT is another good choice from his list of products.
EV also has a lines of powered and unpowered at very reasonable prices. The ELX 112 passive is a much better speaker than your old Yammies, But the thing is, the power your mixer is putting out is a little week. So upgrade the Mixer to a Yamaha EMX512SC or the EMX 1514C. Those will drive any good speaker( EV's, RCFs, FBT's, etc. ) properly. That will leave you with two mains and two monitors, there bare minimum, and no subs.
Alternately, many have gone to powered speakers and passive mixers, especially the newer digital mixers that can have use you an I-Pad as part of the mixing controller. With this setup, it is easy to scale the system. One just adds speakers and subs as needed. The built in power and DSP make these powered speakers foolproof, and get excellent results.
For speakers that sound great and are still affordable, I'd look at RCF ART series, EV ELX, and Alto. A step up would be JBL, QSC, but those are almost double the cost.
Trying to mix passive speakers and powered speakers using a powered mixer is possible, just not ideal.