Thanks, pcqzrd13. Based on the dreampi.py code; I did some digging and the Dell NW147 modems are not recognized by the PI as a serial modem, so it falls back in the script to reading the device through the ttyACM0 port. I suspect that without proper drivers for the usb modem, it won't have v.92 support.
The Dell NW147 when plugged into my windows machine comes up as a Conexant usb cx93010 acf modem, which when searching gets to a page confirming it does have v.92 support.
http://205.175.208.33/products/entry.jsp?id=539 These modems are known as "winmodems".
Running #lsusb on the PI shows these modems with a device id of 0572:1324, which matches the results for a DGC (softmodem) driver.
https://www.linuxant.com/drivers/dgc/index.php Unfortunately the raspberry pi is ARM architecture, so these driver chipsets are useless.
In line 199 of dreampi.py the dreampi script tries to detect the modems present in the raspberry pi, which is using wvdialconf. Running that command with this modem results in "no modem was detected" so I'm assuming dreampi.py ends up at the exception in that command which is to use ttyACM0 at 640800 for the connection.
So I'm pretty much assuming that at this point since the PI doesn't have ARM drivers for winmodems (because winmodems and linux never played well together) it's falling back to the last compatible speed of 33.6kbps for the connection to the Dreamcast.
Yes, I spent a few hours learning all of this for fun...
It would seem perhaps a real usb modem (not winmodem) that's RPI compatible may result in a true faster speed? But man, that's not worth it now. This is no longer a DreamPi issue but an OS/driver and hardware issue from all I can tell.
It also looks like I found the beginnings of the Dreampi project in this thread:
https://www.raspberrypi.org/forums/view ... 2&p=348729