What should I upgrade

Hello,

I'm putting this here because I'm not sure of where to put it. I have a very modest system.

-NAD C162 pre amp
-Aragon 2004 amp
-Emotiva XDA-1 DAC
-Squeezebox Touch/Sonos pulling files off of an NAS
-Silverline Minuet Supremes
-Rel T3 sub, which I actually rarely use

I really like my system, but am kind of getting an itch to get something different. The speakers are pretty much here to stay for a while. So far, they're the best for me, considering my space/placement limitations.

I think I'm also going to stick with the SBT and Sonos. I really like the convenience of not having to deal with disks. I have grand kids.

So, given what I have for a pre, amp and DAC, what should I upgrade that will probably give me an appreciable improvement?

Thanks,
Tony