I've always used Sonitus Multiband Compressor, but I wonder if the LP-64 Multiband would have any additional advantage?

LP-64 hits the CPU pretty hard!!! it's a great tool but mainly for mastering audio.

Could someone tell me if I get the same results with both, or what are the differences between the two?

The LP is a so called Linear Phase compressor (Linear-phase keeps all the frequencies 100% in phase. In other words, all the frequencies pass through at the same speed, resulting in zero phase issues between bands) and I believe the Sonitus is not Linear Phase.
Therefore the LP should sound a little better but at the price of higher CPU consumption/latency.
 

Sheanes
The LP is a so called Linear Phase compressor (Linear-phase keeps all the frequencies 100% in phase. In other words, all the frequencies pass through at the same speed, resulting in zero phase issues between bands) and I believe the Sonitus is not Linear Phase.
Therefore the LP should sound a little better but at the price of higher CPU consumption/latency.
 

Thanks for this explanation of "linear phase".  Just two sentences in parentheses and now I think I get it. I assume that's the same basic approach to the LP-EQ as well,  which would allow for boosting of frequencies without worrying about introducing phase issues.

No, you aren't likely to ever detect an audible difference between them.
 
So why choose one over the other? Each has features the other doesn't, and each one has its own distinctive UI. If you're comfortable with the Sonitus, LP MP's user interface might seem a little obtuse. But overall the LP MB is more sophisticated if you're not put off by the learning curve.
 
Sonitus:
- variable knee
- common (group) settings
- can mute individual bands
- more CPU-efficient
- optional limiter
- minimal latency
 
LP MB:
- bigger UI
- spectrum analyzer
- non-contiguous filter ranges
- per-filter M/S options
- auto-release option
- longer release times possible
- external sidechain
 
 

I'm just getting caught up on the new tools added to Sonar this year. Was sitting on X3 until this past August.
 
The linear phase tools LP-EQ and LP-MB are impressive.  They allow you to have a lot of control, but there is a big gotcha.  Unless you are mastering and can tolerate the huge buffering cost incurred by the LP look-ahead processing, make sure that you run these plugins in non-linear mode if you are tracking or recording, or using anything where you expect real-time latency.  You can still take advantage of the graphic views in these powerful tools, using the non-linear mode (under Precision in the "Expert" menu), without the performance hit.
 
LP-MB video overview: https://www.youtube.com/watch?v=nNHcQX14hWU
 
LP-EQ video overview:  https://www.youtube.com/watch?v=z8ShTTgHkqM
 
More info here:
http://www.cakewalk.com/Support/Knowledge-Base/2016000035/SONAR-2016-04-Update-Notes

This topic motivated me to search for better mixing plugins, where I found these fantastic products from FabFilter.

rogeriodec
This topic motivated me to search for better mixing plugins, where I found these fantastic products from FabFilter.

 
Looks similar to the new LP-MB that is included in Platinum.  Did you even try out the LP-MB?
 
http://www.cakewalk.com/S...R-2016-04-Update-Notes
 
Similarly to the LP EQ, the LP MB has been re-designed from the ground up as a VST3 replacement plug-in for the LP-64 Multiband. It has much in common with the LP EQ, including linear-phase operation (which can be switched to non-linear to conserve on CPU power), the ability to process the left and right channels independently, mid-side processing, and spectrum analysis.
 
http://www.fabfilter.com/...q/using/processingmode

Its extremely powerful, and useful, and sounds great.  Quite reminiscent of the fab filter line for certain.  As far as the op, I cant comment on the sonitus ability to be used as a mastering compressor, where the linear phase stuff really shines in that context, as a processor that likes to handle mixes... as opposed to single minstruments.  An easy way to tell a processors intended use is whether or not it actually has Mid Side capabilities, or... for example, in Ozone from Izotops, theres a "Stereo Unlink" so the sides react to material differently.   A multiband that is meant to throw on a guitar, or vocal for example, may not have these features