ROI. Where is money better spent?

Preamp for sure and the room at the same time. Get a preamp with room correction. Room correction done right helps you hear what your speakers were meant to sound like. 

I agree with ricred1 Preamp or DAC with preamp functionality.  Get eh best source you can before all the other stuff.  I build equipment and I make a DHT DAC and DHT preamp.  As good as the preamp is in comparison to every preamp I have compared it to, the DAC make much more of an overall improvement.  The DAC changed the sound in every system we have auditioned it in much more than the preamp did.  Happy Listening. 

IMHO, I would suggest spending money on the weakest link of the system, however without knowing the system, any suggestion is somewhat like a shot in the dark. Listing your system would help to get you better recommendations

tls49 +1

I spent more on the cables since they are a non-perishable item.