So you can't use the E09K's volume knob when using the Line Out? One of the reasons I'm considering this is that I find that when using the L7 line out dock from my E17 the volume just isn't high enough unless I crank up the gain, which I don't want to do. I'm just worried the line out from the E09K will suffer the same issue.
Yes, you can use the E09K's volume knob when using Line Out, and it ALSO provides amplification. Pre-Out doesn't amp, just uses the knob for volume control and the E17's DAC function. Essentially, Line Out is the whole DAC/Amp package Out; Pre-Out is a big DAC with a volume control knob.
From what I understand, the L7 dock is just for the DAC signal. That's why people get it, is to use just the DAC with another amp. I didn't even know that adjusting the volume would affect anything/the sound when using the L7. I don't have one, so I can't test this whole thing.
To answer your question though, the Line-Out will provide amplification and should provide plenty of power for your speakers.