I run a wet dry sump with bio balls. I really like this configuration as I have an unsubstantiated belief that high water oxygen levels are a great buffer for when other levels get a bit out of whack. In other words having very oxygen rich water allows fish to better deal with other parameters that aren't ideal. The only configuration I have seen with greater O2 inducing potential than a wet/dry sump is the bubbling K1 bed. From the implementations I have seen this looks like the top of the line for bio filtration to me!
But that is just my opinion without any substantial evidence backing it up.
Here is more of my unsubstantiated theory of filtration based more on common sense than any evidence. If you remove the waste before it gets broken down you don't have to worry about the Nitrates the waste would be broken down into. If you buy this theory your daily sock changes are pretty optimal for keeping nitrate levels low.
What is the mesh size of the socks you are running currently?
In my eyes the beauty of the DE filter is the very fine particle size it is able to trap and the lack of maintence in having to clean out the DE filter. I would guess even those small particles are organic and as such will eventually end up as nitrates. So if your over all goal is to keep nitrate levels as low as possible while minimizing water changes a large capacity mechanical filter is probably counter productive to this goal.
Continuing along this line of thought if you don't filter out the debris before the K1 it will either be trapped in the K1 to be broken down or trapped in the DE to be broken down. My way of dealing with this is to use Pothos to remove the nitrates from the water. Whether the debris is trapped in the K1 and shed by the tumbling of the K1 and passed on to the DE to be filtered OR the Debris is trapped in the DE before it reaches the K1... DOES it really matter which is first? If anything I would think you would want the debris trapped where the oxygen levels and bacterial levels are the highest and in theory break down the quickest????
Writing this makes me think about what my filtration goals are for keeping fish. I think my goals are probably keeping a very healthy environment for the fish with the least amount of effort. As such, the large DE filter works very well for my goal. I use a wet/dry sump for biological filtration. This breaks organic compounds down to nitrates. I use Pothos and other terrestrial plants to control the nitrate levels in the water between water changes. I plan on implementing a continuous drip water change system to eliminate the need for water changes altogether. The DE filter gives me incredibly clean clear water with practically no effort. I have tried a Magnum 350, an Ocean Clear cartridge filter and Big Blue cartridge filters. All of them are pretty high maintence and none of them have given me the clarity that DE does.
Does clear water equate to a healthier environment for the fish? I would guess that for the most part it does not. I would guess that for the most part clear water is more for aesthetics than for fish health. I would point out how ever the DE literature that highlight the ability of DE to filter out pathogens and diseases such as Ick. I have noticed a big reduction in the amount of algae in my tank since implementing the DE filter. I attribute this to the DE removing the free floating algae from the water before it can settle and colonize... but this is probably a pretty dubious claim on my part and I would recommend viewing with a good bit of skepticism!
The only practical some what automated way I have seen for removing large debris from the water column is a technology used in the pond keeping world... the cetus sieve.
Which looks to be a marvelous piece of simplistic engineering!
So what are your filtration goals as they pertain to fish keeping?
To actually answer your question: I would be worried about gravity fed DE water filtration eventually backing up and causing problems also!
