1820M
Line Input:
- Input Impedance: 10Kohm
- Max Level: +17dBV (19.2dBu)
- Gain Range -12 to +28dB
1616M
Hi-Z Line Input:
- Input Impedance: 1Mohm
- Max Level: +18dBV (20.2dBu)
- Dynamic Range (A-weighted, 1kHz, min gain): 118dB
- Signal-to-Noise Ratio (A-weighted, min gain): 118dB
- THD+N (1kHz at -1dBFS, min gain): -105dB (.0006%)
The 10Kohm is too low for connecting a guitar directly (not really a Hi-Z input), it needs to be 1 Mohm.
I didn't know this until I bought Guitarrig2 which has the "true" Hi-Z inputs, guitarrig2 sounded quite a bit more dynamic than through the 1820m (bypassing the rig audio interface). Maybe have a look at the unofficial emu forum
http://www.productionforums.com/index.php?f=52 1616M is the better choice of the two now(!).