i just bought all new gear for my r34 gtt also.
I went for the Pioneer, Alpine, Focal mix.
Pioneer Avic-F900BT headunit
Focal KR2-165's for the front
Focal KRC co-axials for the rear
2xAlpine Type-R 12" subs
Alpine PDX-1.1000 Amp
Alpine PDX-4.150 Amp
Bulk pack dynamat