Pre-amp, integrated, new power amp...I'm confused

OK, after posting many threads and reading tons of old threads and reviews...I"m stumped. I have a NAD C370 integrated powering SOnus Faber COncerto's (Home Version), a Cambridge audio Azur 640C CD player going through a musical fidelity tube buffer(my one and only audio source), Cardas Cross IC's and speaker cables. A REL Stadium III handles the bottom end. I love my system, excepy for a little graininess in the top end. I would like to smooth out the sound and make it more liquid and natural. How do I best accomplish this? DO I invest in a whole new integrated? DO i Drive the power amp section of my NAD with a tube pre-amp? DO I invest in a better Source (New DAC or whole new player). I like the sound smoothe and natural...maybe a little warm (Which is why I chose SOnus speakers. I would like to spend no more than $1000. I saw a BAT VK-3i tube preamp available. Am I on the right track with that? Help!