I owned a 39 for 1 year, then upgraded it to 39S (at a $1500 cost), then listened to it for another 2 yrs before only recetly moving on to the Audio Aero.
First of all, the 390S is much better than the 39. It upsamples, has a new board that shares some of the topology in the preamp section of the 32 reference. So no surprise I heard an immediate difference. Deeper soundstage (39 was wide but not that deep), smoother more natural timbre, weightier beefer notes that had more internal resonance and decay, tighter bass - all around better. Not even close.
Anyway, i ran this without a preamp for a couple of years as finances did not allow. It sounds pretty damn good really. Transparent and open. pretty smooth. You'd be no slouch having it serve as a cdp and preamp. Ultimately, i did prefer thesound with a preamp, though. In fact, I have now owned 3 different CDP's with built-on preamps (Wadia 850, ML 390S, and now the Audio Aerro Capiole II, SE) and ALL three sound better with a good preamp.
It boils down to priorities and strategy. I say get the reference CDP, and live sans preamp for a while, then when $ aallows, try preamps (preferrable tubed). This is strategically more sound for the long term, vs getting a lesser CDP and pairing it with a so-so preamp. In that case, you'd always have 2 things to address in the future, and not really being sure which was the 'weaker link", dig?
I enjoyed my ML 390S quite a bit. It's a bit underratd these days, but te things sounded really good. honestly.