Just a few clarifications.
the SONY PCM-M10 holds a short USB port but as far as I understand it is used when willing to transfer the files recorded to the computer.
It holds also one "MIC" entry port and one "LINE IN" port : so I suppose these are analog entries, yes. Still, I don't know if it's possible to connect the USBPRE2 to any of those ports. I guess it is.
With a preamp in front = line in, with mics directly = mic in
You can't use the USB port on the M10 for recording.
I believed that the USB connection was for the power only : the USBPRE2 get the power when connected to the computer. Not only reading your comments : the DATAS run both ways ? Am I understanding right ?
Yes, the USBPRE2 works as an external sound card over USB. The signal contains both sound as well as data to control the settings and goes both ways.
I made few test recordings with the SOUNDMAN OKM II KLASSIC ear plug microphones (binaural) : I connect them to the "LINE IN" port first and press "REC" but there was no recording signal, then I plug them into the "MIC" port and it ran straight fine.
The OKM II doesn't come with a preamp, AFAIK. There is an accessory called Soundman A3, but my understanding is that this is only a battery box with a -20dB attenuator pad:
http://www.soundman.de/englisch/prod_a3_eng.htmSo basically you found out the answer. No external preamp = use mic-in on the recorder.
There is one point I didn't understand : when the USBEPRE2 is connected to the computer what happen to the computer sound card ? I guess, the recording function will be possible thanks the recording software in use (Garage Band, Audacity...) but what about the role of the computer sound card ? Is the computer sound card still active when the USBPRE2 is connected to the computer ? I don't get the point here.
Depending on your preferences when installing, you can simply disable the onboard sound card, and the external will take over (Control Panel > Sound and audio devices...)
Just for the info I looked also at the ROLLS PB224 (117 euros / 151 dollars) since it is in use by some famous US field recordists but a friend of man alert me on the fact the AC port of his broke after few rigs only...
For field use you'd be running on 9V batteries instead of AC anyway, so I wouldn't worry about that part. But most of us concluded that the PB224 is too large and clunky, it's not used much here. There's a lot of gear that offers better value for money, either preamps or plain phantom power (depending on your budget: Littlebox, UA-5, PS-2, Art USB Pre, Art Phantom II...)
Any experience with the MACKIE BLACKJACK ? Are the preamps of good quality ? Because it's USB and a more complete solution than the ROLLS PB224. And cheaper than USBPRE2.
Mackie has a good reputation, but we don't have a confirmation that the Blackjack can run as standalone device (ie without a computer). When preamps are bus-powered only, it's usually a sign of warning.
The predecessor Mackie Onyx Satellite does standalone, can be powered with an external battery, but resamples the analog signal IIRC. Might be a good budget option if you find it second hand and don't mind the bulk.
But if you put it next to the Littlebox, I personally value the stealth factor much more.