Best upgrade for the money ?

Rob: Forget about the power cords for now. They will make a relativily minor improvement $ for $ as compared to speaker replacement. You need to decide on your speakers before considering a DAC or anything else. Everything is system dependent in order to achieve some sort of synergy. You can buy good used speakers starting at the $750 range & approach great at the $1500-$2000 range. As an example...I saw a pair of Totem 1's on audiogon for $750 which will blow out your Polk's, however they are limited in the low end. You also need to be care with the efficiecy of the speaker, as I'm not sure how many WPC your amp puts out. Hope this helps.

Get new speakers and get some reasonable power cords later.

Might want to look at paradigm speakers (great bargains and I have seen several steals here on AG)and a power condition (just for the general protection and help in sound. made a great differnce- If you want a reasonable price, monster 3500 is fine - you can get for 1/2 of list on AG or eBay

I agree with almost all of the above suggestions, but no one has yet chimed in to say that one of the best upgardes you can do is to add phono. Get something like a Rega Planar 3 with a Grado or Sumiko Blue Point. It will KILL you Micromega. Even more than speaker placement, vibration isolation, and acoustic treatment of your room, adding vinyl will be a gestalt. You may have forgotten (or, perhaps more likely, never known) how good records are.

I've seen a lot of good advice here especially regarding roomtreatment and vibration control. After that's taken care of my guess is that either splitting off your pre-amp functions to a good unit - tube or solid state- will make a really big difference. If you're not ready for that step, then a speaker upgrade will also make a tremendous difference. I've had a Micromega stage 2 for 5 years and while It's not state of the art, my feeling is the gap is not as large as some would like you to believe. I swapped in the Meridan 508.20 recently, and while it was better, the change was minor compared to what adding my Audible Illusions pre-amp in place of my intergrated's pre(WOW). If your Sim is better than my Arcam 9 was, then I'd start with the speakers.