Budget amp that will give Magnepan 3.6Rs better depth of soundstage

I have 3.6Rs and using Emotiva UMC200 pre/proc and an Outlaw Audio 7100 in a 14 by 14 foot room. So I don't need to turn the volume up to massive levels. The amp will do 100 watts per channel into 8 ohms and 165 watts per channel into 4 ohms. I have been thinking of getting a separate two channel amp for the 3.6Rs. I have read that it takes lots of current to get the best soundstage with instrument placement and depth. I am getting wide soundstage and good sound, but the depth is somewhat muddied enough to not get instrument placement. I am looking for a two channel amp that will give me more of the potential of the 3.6Rs, but be able to be purchased for less that $750 used.  Is there any amp that will be worth upgrading to for that kind of money or do I need a new pre/proc as well?