With only 6 days, I recommend you pick 1 or 2 spots, and no more. Either focus on La Ceiba & Roatan. Or just La Ceiba & the surrounding area (river/jungle/beach). Or just Roatan.
No volcanos nearby. Jungles, river trips (rafting, hiking, etc), wildlife spotting are near La Ceiba.
The ferry to Roatan runs 2 times a day. It takes about 2 hours (+/-) from La Ceiba. If weather is really rough -- it can be delayed or canceled (not often, but something to consider if you are tight on time).
If you rent a car, you'll have to leave it in La Ceiba -- you can't take it on the ferry to Roatan. Better to return it than to leave it in a lot that will get stolen.
Personally, I didn't like La Ceiba and don't think it's worth a visit -- but the surrounding area is (beaches/jungle/river/etc). Everyone is different though - so I'm sure you'll hear differing opinions!