HELP turntable newbie, project genie setup

hey, complete newb but just taken the plunge and bought myself a propper turntable instead of the 60s portable thing ive been using!

my setup is
NAD C320BEE
NAD C5432 cd (not that it matters!)
Tannoy mercury m3
spanking new project genie mk 3

so i got the turntable and set it up as best i could following the instructions and it just about plays when directly through amp but i have to have the amp full blast to get a just about listenable level out of it, and even then the sound is very flat and empty, the bass and treble nobs did nothing to the sound, now
from what ive read i gather i will need a preamp so ive ordered one just to get the thing up and running, its a behringer p400, my question really is how important is a decent preamp in getting a good sound out of my records? how much will this preamp actulally improve my listening? will it make it so i can adjust the bass and treble on my NAD amp?, if ive made a massive booboo by buying cheap then could anyone reccomend one which would complement my system, baring in mind like most people out there im not exactly made of money and theres always a budget, as you can probabily tell from what i already have im no hardcore audiophile i just love music and want a reasonable system to listen to it on!

thanks in advance-jake

Your RPM 1.3 uses an Ortofon 2M red cart, which is MM, so it's a high output cart, but you will still need either a receiver/integ amp/control amp with a "PHONO" minput, or you will need an outboard phono stage to use a "LINE IN" input on your existing system if you have no PHONO input already. As Jan noted, this is why your TT sounds off.