Mav, Thank you for your interest, and those are good questions! We are not performing pre order sales for this product, but the HDV 820 will start to be available in Mid-September and you will be able to buy it directly from our online store at that time. The output impedance is approximately 40 Ω. At recent audio shows, people were connecting many different headphones to the HDV 820. This is a powerful desktop amp designed primarily for full-sized headphones, but we can discuss more about IEMs and low-impedance headphones in the Questions and Answers thread soon. For connecting two headphones at once, we recommend connecting two of the same headphones to the balanced outputs so that there isn't a volume difference, however there was no damage from connecting a headphone to the balanced and another to the unbalanced (single ended) ports at the same time. Keep checking Sponsor Announcements and the Questions and Answers thread for more info as we get closer to availability.