To Preamp Or Not To Preamp Vac 30/30 MkII

Hello everyone. My current system consists of Vac 30/30 MkII, Wadia 860x and Audio Physics Virgoes. I am developing an itch to upgrade by adding a preamp in the 2-5 K range used and possibly upgrading Vac to Mk III se status at VAC for $2400. Please help me decide which will have a more profound improvement and if you have a similar system what brand of preamp, interconnect and speaker cable synergy you have found to work best. I listen to mostly jazz, male and female vocals and some rock. Yhanks for your input.