2.1 / 2.2 Request for Amp Suggestions

Recently, I purchased a Rogue Audio Cronus Magnum II and a pair of Magnepan 1.7s.

There's a noticable gap in the bass that I'd like to rectify. I don't use the system for TV/movies, though I probably will at some point. I prefer accuracy over thunderous response and am looking at the Magnepan DWM panels. My concern is that the power in the amp is definitely not enough to drive the DWMs, not to mention that the amp is already wired for the 1.7s at 4 ohms, so mucking with the impedance will probably result in blowing fuses and tubes.  The room size is on the large side. The 1.7s and amp seem to be matched right now, both for power and resolution, especially after rolling in a Telefunken preamp tube and getting the 1.7 placement pushed out to nearly 5 feet. Again, I'm absent the bass I want and am unwilling to muddy the 1.7 sound by pushing them back toward the walls. 

With this in mind, I'm thinking about using the preamp output on the integrated amp and connecting it to a secondary unit. What kind of amp should I use? I don't need an integrated amp as unit #2 and am struggling with the price of a Rogue Audio M180, even used. What would you do in this situation and why?