My 2 cents:
Wait until you get your Ody, and listen to the system to see what you think is lacking. This topic has been discussed ALOT in this forum, both in Kelton Sub threads and in the Pioneer 1695 thread.
I have not listened to the Kelton sub, so can't comment on that, but I can say (as others in this forum would) that replacing the factory speakers, particularly the fronts, will improve the overall sound quite substantially. The Pioneer 1695 at <$80 online is a hard to beat upgrade for the $$. Not only do you get better bass response, but imaging and HF response is alot better than factory. I've installed the 1695 in an Ody and think for most people, they would be sufficient.
So, I'd say, wait, get the Ody, and listen; esp, when driving on a highway. If you think the sound is good and just needs low end oomf, go with the Kelton. If you think something else is lacking, you need to shop for some speakers.
Besides, H and A is really fast with orders, so getting a Kelton shipped to you quickly is not a problem. Typically they ship same day if you order in the morning.
One last comment regarding the divergence of opinion between Steve and Adam's experience. I'm not sure if Steve switched out any of his main speakers, but seeing that Adam has, this is a possible explanation for the difference of opinion. High frequency response dramatically affects perception of the "cleanliness" of bass. A great example of this is that many types of drums have a higher frequency "leading edge" to them. Those with home theaters at home can try this out by listening to their subs alone, without the mains on.
When auditioning subwoofers at a hi-fi store, it is a definite no-no to switch main speakers, makes judging just the sub very difficult.
Again, very long winded, but hope this helps someone...
-SJ
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DEP '01 EX no-navi