how can a 480 decks ssb get The Omniscient medal? what scan modules should be installed what buffs what race etc.

Well, according to the wiki, it requires at least 9317 scan. Assuming you have the explorer buff (20%), stryll seeker (10%), UST (6%), beacon (15%), tachyon and subspace (+50, +175), then you need a little more than 6.7K scan from mods. If you have other percentage buffs it's obviously easier.

Mission rewards + base scan = 61 scan/0 decks/0 decks total
Merged Datanode = 240 scan/21 decks/21 decks total
Continuum Analyzer III (3) = 3840 scan/384 decks/405 decks total
TitanProxy (1) = 100 scan/40 decks/445 decks total
T'Vul's Core (1) = 60 scan/20 decks/465 decks total
Co-Align Signal Processor (1) = 80 scan/15 decks/480 decks total
Sehrin = 149 scan/0 decks/480 decks total
Trovar = 179 scan/0 decks/480 decks

4709

1.2 * Protogrid Access
1.2 * Explorer Profession
1.15* Continuum Beacon
1.1 * Stryll Seeker
1.06 * Sensory Calibration
1.05 * Trovar
1.04 * Proxy
1.04 * T'Vul thingy.

10,326 scan with 480 decks = Omniscient.

Also, if there's a race change, you know the person is going to be a Sillix Explorer, so you're actually working with 528 decks, but yeah -- you can do it with 480 decks.

i did a bit math so :

Mission rewards + base scan = 61 scan/0 decks/0 decks total
Merged Datanode = 240 scan/21 decks/21 decks total
Continuum Analyzer III (5) = 4800 scan/480 decks/501 decks total
Stryll Hunt Sensor=50 scan/10 decks/511 decks total
Stryll Prey Tracker=75 scan/14 decks/525 decks total


total scan : 5226

Subspace Seeker +175
Tachyon Cylinder +50
1.2 * Protogrid Access
1.2 * Explorer Profession
1.15* Continuum Beacon
1.1 * Stryll Seeker

total buffed scan : 9929.5

i think this is an easier way for sillix explorer with 528 decks <480 base decks>

How i did it (436 decks, 480 with sillixx)
http://galaxylegion.com/forum/viewtopic.php?f=4&t=31929&p=394857#p394857