I can get the 6’s for $200 or the 8’s for $400 (both used). Is the punch of the 8’s enough to pay double the price? I’ve been having a hard time getting mixes leveled because the monitors I’m using have no low end. I find myself raising the gain on subby tracks too much because of the perceived loudness. I’ll also be using them for production.
Id say it depends on the style of music you produce and the treatment size of your room. To much low end in an improperly treated or sized room/setup can make the bass very muddy and you lose the purpose of it entirely in my experience. If these are your first pair, and you are in a small bedroom studio, id just go with the 6’s If you have the room and bit more cushion, id say the 8s.
i can tell you that $400 for used 8’s is a terrible deal. you can get them new for $425 the majority of the time. musiciansfriend regularly has 15% off deals. even it it’s a 1 item discount, just order 2 separately. i did that at guitar center when i got my 8’s (which i got for $170 ea. brand new btw).