My view here is if you really need a headphone, get the wireless headphone (from CDRing?). It should have an RCA input for your audio source (except from LD330 which doesn't have audio out). I suppose this is what you originally needed in the first place (so as not to annoy other people in the house). Am not sure if these wireless headphone units have wired headphone jack as well.
Actually, I don't agree if you buy an external power speaker instead, if you just needed the headphone. Although there are some powered speakers with headphone out jacks. I have a Philips powered speaker set that has a headphone out jack as well. Other than the headphone requirement, why an external powered speaker when you can make use of the LD330 internal speakers.
Unless you wanted a more solid sound, you can opt to get an HTIB instead, which might have headphone out as well. Am not really sure about this headphone out thou. I guess you have to confirm this part. But some compo (mini/micro), I believe have headphone out jack.
Hope this helps.