so what about this, besides being smaller and newer and shinier, would entice me to sell my 671 and get this instead?
edit: i've read a bit of the thread, but can't seem to see the differences between the two except that this uses SD cards and the 671 uses CF.
Well, in terms of form factor, it's less than 1/2 the size and weight, the display is better, and the internal battery setup is much better ergonomically. From a powering perspective, you only need half as many AAs to run it, and they fit directly into the deck, not inside a sled with 2 contacts known to have issues for users. With just four 2650 Duracells, running line in, I have run it for hours and still had a full charge showing on the display. Mic in, using the preamps, users have reported exeeding 5 hours with a single set of AAs. So, my 670 has been retired to the home system to use for transfers of my old DATs, since I got my modded 661 at the end of March.
Operationally, I think the biggest differences are both a plus and a minus. The minus is that there is no digital out. But, unless you are taking a digital in from a V3/Apogee/AD2k, the digital output on the 671 is not functional anyway, so it's not that big of a loss if you are using the A/D on the 671 you now have.
The big plus, the main factor that sold me, is that the 661 is the only flash recorder besides the SD702 that has a true professional XLR line input that has +4 db pro line level sensitivity. Your 671, for example, has a consumer level line in that is 14 db more sensitive than an XLR line in, and therefore cannot accept a hot input from an externa preamp or soundboard without clipping.
Also, with the HDP2, FR2LE, and the 671, modifications to improve the preamp only improve the mic input, the line input is still stock. With the PMD661, the modification is made to the XLR inputs, so both the line in path and the preamp path (mechanically switched) have upgraded inut capacitors and opamps, with just an additional set of upgraded chips for the mic pre when the switch is moved to mic in.
Hope this helps you decide.