As long as you have sufficient DSP resources available you can use the same FX multiple times
See here for an older thread on this topic by Line6Miller: http://line6.com/support/message/187820#187820
For sure, you can use 2 noise gates in the pod HD 500, place them wherever you want, and so on!!!
Please, check this another thread about a djent sound with POD HD series: http://line6.com/support/message/187835#187835
Sure you can! Check out my soundcloud page, i've recorded some DJENT clips using HD500.
kake83 has a cool djent preset in the customtone patches, also check out chimp spanner's video: http://www.youtube.com/watch?v=Vo1sVHDlZII&list=UUsxGHznKmD6NaAyCABd5ebg&feature=plcp
+1 to Nick_Mattocks.
You can use mulitple instances of the same effect, provided that you aren't using alot of other DSP intensive FXs/Amps. Check out the communities suggestions above for "djent" type of tones.
Someone's been looking at Bulb's rig. ;-)
I get my Periphery tone by running a noise gate after a distortion pedal effect, which doubles as a compressor. So instead of doing the 4 effect "comp - gate - dirt - gate" setup, I find I can get away just going "dirt - gate".
It sounds pretty awesome.
Getting awesome djent tone from the unit isn't as easy as it should be, but it will djent very well when setup to do so. I wrote a guide on it. See here:
I should specify - you CAN use two gates if you really want to. You could run 8 gates if you want. I only run one because I find there's no real gain in running more than one. if you wanted to run two, i'd put the first gate before the compressor - that's it's job to make sure it doesn't let any compressed tone through.