I've been having the same kind of personal debate since I can't afford both a great grinder and the machine I really want right now. Should I get the grinder I want, and then get a less expensive machine, or get the machine I want and a less expensive grinder?
For me it's come down to this decision (and I'd love to hear what other people think about my logic): Do I want to be able to get consistently good results from any coffee I try, or would I rather get great results from some coffees and OK results from others?
1. Some coffees just taste much better at higher or lower temps, and sometimes have narrow ranges that work well - or I just have a preference for the taste of some coffees at certain temps. Getting the machine dialed in and consistently hitting those temps should be easier with a DB. So if I want to try a new coffee every week, or a couple new coffees during the same day a DB will get better results easier, especially for some of the trickier coffees.
2. A good grinder will give you better results from any coffee, so as long as the beans I'm using aren't particularly demanding temperature wise, or just work best at the temps that are easiest to get consistently, a "titan" grinder plus good HX will give me tastier espresso. The trade off is that it will probably be more difficult for me to dial in temps consistently for some coffees, and those shots will be more hit or miss.
So, do I want to play around with lots of coffees and try different temps (easily), or do I want to know that I'm getting great results from some coffees and have to work harder, or settle for a little less consistency with others? Personally I'm also looking at the Duetto II, but considering a "titan" grinder + Bezzera BZ07 - there's the chance that that combo would deliver good enough results to keep machine upgraditis at bay for a long time, of course if I moved and was able to plumb-in I'd be kicking myself for not getting the Duetto - just one more thing to consider
