That’s not synthesized at all, it’s articulated very well, you can hear palm mutes and whatnot. It might be a really good sample library at best, but it doesn’t sound synthesized to me at all. Unless you’re talking about the synth lead… heavy distorted rhythm guitar is hard to impossible to synthesize well because what makes it sound good is the different ways you can articulate it. Palm muting, different picking and strumming techniques, all ups, all downs, alternating, different pressures of your palm, the way you release your palm for opens, you just can’t synthesize a good performance.
If you need guitar samples I have several guitar .xrni’s up in the downloads section, here’s on for heavy rhythm guitar:
http://forum.renoise.com/index.php/files/file/50-power-chords-std-processed/
If you plunder the internet you can also find some really nice “DI” samples (I have a DI version of what I just linked up here somewhere) which is just the raw guitar recorded straight into an audio interface, which allows you apply your own effects. Whether you are trying to synthesize (if you really want to try, FM synthesis is your best bet) or using samples or a real guitar, the formula for heavy guitar rhythm sound is the same, it’s all about the processing effects (as opposed to synthesis). Distortion(if any)>Amp>Cab is the chain you want to use. With a good enough amp sim you really don’t need pre-distortion. I only use distortion to drive clean amp signals when I want a janglier lighter distortion. If I want heavy, I just use an appropriate amp sim.
http://www.igniteamps.com/en/audio-plug-ins
This will get you pretty much all the plugins you need to get started. Get Emissary and Nadir. Put Emissary on the lead channel. Nadir is a cab impulse loader, and the amp sim will sound like shit unless you process it with a cab impulse. My favorite set to use is the Catharsis impulses, which are free but seem to have disappeared from the internet. PM me your email and I can send them to you though.
Here are some DI samples for you:
http://bedroomproducersblog.com/2012/10/13/thrash-di-a-commercial-metal-guitar-sample-library-by-sampleoddity/
Also I might be able to record some guitar for you if you’re able to compose what you want with samples but aren’t satisfied with the sound.
edit: Oh I thought Thrash DI was free, but it is not.
edit2: Oh here we go, free version:
http://www.sampleoddity.com/thrashdifree/