Loss of sound level with sub--low inputs

I have been using my sub with Kimber speaker wire connected to the high level inputs and am somewhat familiar with the sound when configured that way. Decided to try using the preamp outs on my amp using a very good quality interconnect to connect to the low input connectors on the sub. It seems that there is a very sizeable signal loss, and not much response to changes in volume on my amp--an Arcam Alpha 8R. Changed interconnects and the same thing--the punch and presence are gone. What gives?
I have had similar experiences and always found that high level connections rendered better results for music when I was using a sub. In my case the sub pre out was really only effective when there was some .1 info on the software such as DVD's etc.
I did the exact thing as you although the other way around...I'm much happier with the sound now.