I really don't like to see people get rid of equipment they like. In your case, though, you seem to really know what you want.
"I am looking mainly for detail, wide bandwidth, tonal neutrality, soundstage and imaging."
For something not too expensive, I can't think of anything better than an Ayre K-5. Your above quote is exactly what it sounds like. With the Ayre, you won't miss your ARC at all. (Just to be clear, I'm comparing the Ayre to the SP-16, and nothing else. I'm not saying its better than all ARC preamps, just the one that the OP has. Also, my comments are just my opinion, and are not meant to be taken as fact.)
"I am looking mainly for detail, wide bandwidth, tonal neutrality, soundstage and imaging."
For something not too expensive, I can't think of anything better than an Ayre K-5. Your above quote is exactly what it sounds like. With the Ayre, you won't miss your ARC at all. (Just to be clear, I'm comparing the Ayre to the SP-16, and nothing else. I'm not saying its better than all ARC preamps, just the one that the OP has. Also, my comments are just my opinion, and are not meant to be taken as fact.)