Upgrade advise needed please

I've asssembled a pretty decent system that started out as a HT system and is evolving into a combo HT/music one with more emphasis on music. I can only afford to make 1 last upgrade for awhile and need advice in which direction to go. I have about 1K to spend and don't know if that should go to a different preamp or a good outboard DAC. Which of these will yield the best improvement. I currently have all Vienna Acoustic speakers (Beethovens, Maestro & Haydns) with a Proceed AMP2 & B&k amp along with a B&K Reference 20 preamp processor. Sources are a Elite DV-05 and PD-65. Would a good preamp with a processor loop (keeping the Ref20 for HT)be better, or would adding an outboard DAC yield the most sonic improvement? I appreciate any advice you can give as this will probably be my last upgrade for the time being. Thanks all!