I have now had my NH700 for just over a week, and I am extremely happy with it. The sound quality and the solidity of the build quality (despite the device being all plastic) significantly surpass my original expectations, and I have instantly become a minidisc fan! :smile:
I spent 8 hours on trains in Italy on the weekend, including 5 hours on noisy regional train, and listened to my minidiscs the whole time. Using my old Panasonic earbuds (open back, and with the equaliser on), I found the volume to be loud enough for my tastes on settings around 18/30 - 20/30. I may invest in some isolating earbuds in the future, but I certainly have no problems with the output power of the NH700 for my purposes!
Thank you all again for your helpful and accurate comments.