not really. a 6 ohm and 4 ohm together will have an impedence of 2.27 ohms. although your head will still deliver the goods at this (it will diliver more power actually) it will be generating MUCH more heat and working under stress it isnt designed to work under, and will therefore probably overheat and break pretty quickly
for a four ohm head you best bets are a single 4 ohm cab or two 8 ohm cabs
you cxan also use your 611 on its own but your amp will be giving out slightly less power because of the impedence. it'll be nearer 400/420 watts
i'll give my own explanation of impedence and hopefully this'll help you see why this all happens
bass cabs are usually rated at 4 ohms or 8 ohms, the 8 ohm cabs having twice the resistance.
lets take your head as an example. its rated at 500 watts into 4 ohms. therefore if you connect it to a single 4 ohm cab you'll be putting out the amps full 500 watts. you could also connect it to a single 8 ohm cab. in this case due to the increased resistance the head will only be supplying about 350 watts (70% approx of the powerout under its reconmended load). despite this the head will be under less stress and will be generating less heat (this doesnt really matter as its been designed to be able to cope with the stress running at 4 ohms will generate)
you could also use 2 cabs. using two cabs of the same impenence rating halves the resistance. think of it this way...the power from the amp has more speakers to come out from.
for example
2 X 4 ohms = 2 ohms
2 X 8 ohms = 4 ohms
again lets use your head as an example. with the two 8 ohm cabs it will produce the 500 watts same as the single 4 ohm cab. there will however be more speakers so an increased surface area of cones/ more drivers which will make the sound appear a bit louder.
however if you connect two 4 ohm cabs the head will be supplying power to cabs that are providing little resistance. because of this the head will work harder to generate enough power to propperly power the drivers. this will lead your 500 watt head into generating nearer 650 watts. this may sound good (extra power
) but the head isnt designed to work at providing so much power. because of this the head will generate a TON of heat and all of the componants will be working under far more stress than they were designed to work under. this will cause your head to eventually blow up
boom no more head
the 6 ohm may sound like a strange impedence for a head but warwick made it to compliment their 1000 watt heads. it'll bring the power down to about 900 watts but even though the heads are losing power i believe warwick designed them this way so they could run 6 speakers instead of the conventional 8 speakers in the traditional mother f**ker speakers (i presume its hard to make a 6 speaker cab run at 4 ohms)
i hope this makes things clearer
