to achieve an upright bass sound, you're better off stuffing a sponge bwt the bridge and pickup and get your strings as mucky as possible. and pluck where the neck meets the body
Sorry for not really answering your question, but:
The best double bass sound not coming for a double bass I have ever heard comes from an Ashbory Bass.
Biggest disadvantage being that there is only one Ashbory player in Singapore (me) which makes it difficult to get silicon strings, but this will be the topic for my second post in this forum ;-)
For your reference:
http://www.fender.com/products//search.php?partno=0350100306
http://www.dearmondguitars.com/ashbory.html
http://en.wikipedia.org/wiki/Ashbory_bass
Cheers!
Either get a fretless with flatwound strings or switch to tapewound strings.
The EBS Octabass will NOT get you a double bass sound.