As I said before: This gives a good overview of how to distribute processing accross your cores:
http://support.apple.com/kb/ht3161
or look at bounce in place, freeze etc as other free options.
This gives a good overview of how to distribute processing accross your cores:
http://support.apple.com/kb/ht3161
You could also consider freezing or bouncing tracks to save processor power or use less intensive plugins, optimise the plugin settings etc..
If that's still not enough then you should get a computer with as much processing power as you can afford. These benchmarks give you some idea of how different models will perform:
http://browser.primatelabs.com/mac-benchmarks
https://www.gearslutz.com/board/logic-pro-x/371545-logic-pro-multicore-benchmarktest.html (you need to read the thread for newer models).
Logic X does not handle multi-core processing differently.
You will need to loop the samples.
https://help.apple.com/logicpro-instruments/mac/10/#lgsifc864a8c
https://help.apple.com/logicpro-instruments/mac/10/#lgsifc862479
In general you can only open projects from previous versions. Perhaps you got lucky before and the newer projects are using some different features, or it could be the way you are transferring them. I doubt there is an easy solution except for updating your Logic version.
Logic only supports Audio Units (.component files).
Is Amplitude not showing at all in the AU manager? Does the plugin version you are using support OSX 10.5.8?
The setting to adjust latency is called I/O Buffer Size. It can be found in the menu Logic Pro>Preferences>Audio. Set it to a smaller size for lower latency, but if you set it too low you may hear some problems (it mainly depends how fast your computer is).
Input monitoring in Logic is called.. er.. "Input Monitoring".
True, but I would prefer it wasn't there at all. It is strange that it isn't there until you use a group, and then it appears and you can't hide it again. Since I never use that window at all it is just clutter.