There are MANY new processing units on the market. I'm not up to date on all of them but I hear the Audison Bit 10 is actually pretty slick. I have a Bit1 and like it. I've owned a JBL
MS8 and I hated it with every fiber of my being.
OP, to answer your question about different ohm drivers, the answer is simple...a higher impedance is ALWAYS fine/safe. A lower impedance is sometimes risky.
Think about what's happening like you're riding a fixed gear bicycle (one where the pedals MUST spin if the rear wheel is moving). Pedaling faster when the impedance is low allows you to make good power. However, there comes a point where the impedance is so low that you're spinning out of control and eventually you'll hurt yourself because you simply don't have the ability to pedal that fast. The same happens with the amp, lower impedances yield more power but the amp has very specific power output limitations. If you ask the amp to make more than those limits it will fail.
Running an 8ohm driver will actually make things EASIER for your amp. Yes it will yield half the power but it's not as serious as you think. An 8ohm speaker that is 87db efficient @ 1w/1m will play just as loud off 50 watts as a 4ohm speaker that is 84db efficient @1w/1m getting 100watts. The reason is the general rule that to gain 3db of output you need twice the power.
What's even more interesting is that most 4ohm speakers aren't as efficient as you think. You may see efficiency rated @ 2.83V/1m. 2.83 volts on an 8ohm load is exactly 1 watt of power. So when you see this rating on an 8ohm speaker it means 1w/1m. However, on a 4ohm speaker you're dealing with half the impedance so 2.83V makes 2watts of power....TWICE THE POWER! That's a little trick many manufacturers use to "inflate" the efficiency ratings of 4ohm and 2ohm speakers. On a 2ohm speaker it's really getting 4 watts...put that in your pipe and smoke it!