Guitar sounds good - just add more tracks for better "wall of sound" effect and maybe a bit more low end. [edit] scratch that low end comment i forgot that i have very crappy headphones [/edit]
Synth - yucky yuck yuck yuck - try some free ones at kvraudio.
ps. IMHO Dimmu is one of the best sounding bands on our planet so it (probably) will be VERY hard for you to sound 100% like them.