Bruce, what you report hearing about a 10db boost in the LFE channel(for certain technical reasons)when processed by the receiver is essentially correct. However, the 520 and all other HT receivers are designed to do this, whether in DD or DTS and whether speakers are set "large" or "small". Why do you say that your 520 "..is only able to amplify the LFE when the front speakers are set to LARGE"? Unless your 520 has a defect on DTS only which I've never heard of before I don't understand the problem.
You have a good sub and it's good procedure to set all speakers as "small"(regardless of how big they are)and the 520 crossover at probably 80hz. The crossover on the sub would then be turned up to the max to get it out of the way of the 520 crossover. This reduces the strain on both the main speakers and the amps in the receiver which drive them.
