If that's what you have to do to get a decent master, then that's what you have to do. I've had cases where the vocal is jumping all over the place, so a multi-band compressor is needed to get it under control without touching the bass or whatever, then I still needed a little wide-band compression to help the whole thing gel a little bit. In general, multi-band compressors are reserved for emergency rescue work where there's problems with the mix and you can't get a remix.
... not sure if this not destroying the dynamics range..
this is the important point. Ensure that it does not destroy the dynamic range with (true) A/B comparison (on same level) and if it still sounds better. If so, go for it. There are no rules or advices... only your own experience "try and listen" might give you a direction.
I agree. At the end of the day if it sounds good then go with it. There are people on GS who say they 'NEVER' use multiband compression. They must always get perfect mixes then. Because in some cases nothing will work better than a multiband. If Dave Kutsch uses multiband (t-racks as a matter of fact), then it must not be THAT taboo.
If I can make it just a couple more days, I think I'll have an entire calendar year without using a maul-the-band compressor once.** Not even for really crappy-sounding problematic stuff that maybe could have used it.
So I guess I'm not the guy to be answering this question anyway...
** I'm not counting when I've used maul-the-band compressors as frequency-conscious expanders... That's much more common, though still relatively rare.
But back on subject -- If that's what the mixes are telling you to do, go for it.
A multiband compressor is not a beginner's tool much like a chain saw with a 3 foot bar is not a beginner's tool. That said, a MBC effect can be dramatic or subtle as determined by the user. It is a useful device to have available but it helps to really understand what compression is and how it can be used as a shaping tool both spectrally as well as dynamically. Much like any tool in the kit, sometimes it's not applicable, sometimes it's just the ticket.
Series compression may be useful combined with shaping EQs but stacking compressors is more exponential than linear in terms of its effect on dynamic range. It's easy to overdo it quickly. Level matched A/B is your friend.
Light multiband limiter (with intelligently set x-over points) with light broadband limiting after is in my experience a great way of taming those 4-5 overs per track you often get with very dynamic acoustic music with minimal side effects. I normally use this to give me an extra dB or two at the end of my chain.
I very rarely use multiband compression, as said above only when there's something which really needs taming in the mix and it's not possible to get a re-mix.
I use multibanbs and single band compressor in combination all most everyday.
I master only electronic dance music and use an MLA3 for bass control fellow by a Phoenix to glue the track together and repare the damage induce by the crossover phase shift of the multiprocessor.
And of course a track were the bass perfectly mixed I will never use multiband, but I receive lot of dance music made in small monitor and no room traiment, so then mutiband and single band compressor in serie become a very usefull combination.
Be aware that the total gain reduction between the two compressor never go over 2 to 2,5db usually 1,5 db and this for 0,5 db on the MLA3 and 0,5 to 1 db on the Phoenix.