All,
When I built the prototype, I was listening to a pair of ALO re-wired HD650s and they sounded great! I'm waiting for Ken to get some HD800s in stock and I'll be sure to order myself a pair. I suspect the HD800s are going to be amazing with the Isabellina HPA. But I must say, the re-wired HD650s sounded really nice. I also have a pair of K701s, which seemed to offer some more detail and clarity vs. the HD650s, but didn't quite have the filled-in bass that I was craving. Overall, the HD650s were warmer and had richer tone, and Ken's cable helps give them a little more top-end extension.
Ken also let me borrow his re-cabled Ultrasone UE-9s and the Grado GS1000s - both worked very well. I think the UE9s have more bass than I'm looking for (but were a lot of fun, especially with pop, electronica, etc.). I also heard the D5000s and they were also really nice with the HPA. Again, plenty of bass if you like bass, and the highs were very detailed.
And there are so many more out there that should provide excellent results, such as those listed in the Amphora threads as HeadphoneAddict mentioned above.
Yes, headphones that sound great with the Amphora will sound great with the Isabellina HPA. The 12V SLA battery power in the HPA seems to give a little more weight and authority to the sound vs. the smaller Li-Ion battery in the Amphora, and the Isabellina dac is a beautiful match with the headphone stage, and also superb on its own (using the RCA outputs) feeding other equipment. I fed the RCA outputs to a Signature 30.2 feeding K1000s - SWEET! (if you like unique open and spacious sound of the K1000, which I do!).
For iPod users, I recommend the Wadia iTransport so you can feed the digital output directly into the Isabellina HPA. The iTransport will fit nicely on top of the HPA. Otherwise a direct USB connection from your computer (or coax/optical from your CD transport) will do the trick.
So pretty soon we'll start a new Isabellina HPA impressions thread. Units will begin shipping this week (and next week) as promised!
All the best,
Vinnie