tied:
ASC tube traps (locally): four at 4'*16", six at 3'*16" and 10 diffusor panels thrown in. very shoddy condition, but nothing a day of work couldn't fix. the ASC were a huge improvement over the JRisch Q&D tube traps i was using.
and
Audioquest Redwood speaker cable: i'm ashamed to admit how these expensive silly wires transformed my rig, but they did (rediscovering music). best cables i've heard. remarkable upper midrange / treble clarity, great bass control and articulation, very very quiet, excellent staging, tonally mellow.
(very pleased i'm OFF the merrygoround where it comes to cables (Redwoods) and power conditioning (Weishi))