If you buy Cubase 7 you get a license for that, which is also a license for all previous versions. Whether C6 can be still downloaded from the Steinberg ftp I don't know.
--- "If anyone owes it all to Bach, it's God" - Emil Cioran ---
SOFT: (All 64 bit) | WaveLab 8.5.20 | Cubase 7.5.30 | HALion Sonic 1.6.3 | Win7 Pro - SoundCloud
HARD: i7-950 | Asus P6TD | 30GB | Tascam DM-3200 | DigiMax48 | Midisport 8x8 - SoundByte Studio