Most bang for the buck?

I wasn't sure which category to post this under....but here goes:

I will be doing one of the 4 upgrades listed below in my life (5yr plan). I will possibly do all 4 eventually. I invite input from the knowledgeable group as to which would provide the biggest improvement overall.

My electronics are: HCA-2, Carver Sunfire preamp, Music Hall 25 Mod +, Epicure 3.0 way cabinets that have completely redsigned drivers and crossover from Meniscus boys with a pair of Vandersteen 2wq's.
1. Biamping the mids and highs, or left right? with another HCA-2
2. Getting a power conditioner
3. Upgrading to a PCA-2
4. Modding the HCA.