You shouldnt need to worry about it unless your run is over 100 feet. Preamps, unless you are very specific in getting one with low noise, and bandwidth that covers scanners, will cause so much interference and intermod that you will regret it. 100ft of RG6 at 900 Mhz is only about 6db loss. The only way I would consider one, would be if I lived way out in the country, with no transmitters nearby to cause interference, AND if you were able to pick up your desired station(s) with the scanner in the attic, but NOT with the antenna in the attic after running it through the feedline.
My ST2 with the coax run is able to pick up repeaters on UHF 60 miles away. While putting it in an attic will cause a little attenuation of the signal, I dont think a preamp would be nessessary.
Ok I think iam gonna do that then the ST 2 is reasonable price 50 bucks on ebay and I got lots of coax in the walls this way I can move the scanner to different locations in the house if need be thanks for the help guys !!!