A caution here - wideband preamps (without any way to adjust the gain) are liable to cause more issues with increased noise and overloading in certain situations (urban areas with lots of RF in the air are more prone to this...). Too certain scanners (GREs are more guilty of this...) can and do overload and desense when signals are too strong to be handled.
Your best bet here is a better antenna, and most importantly, low loss coax. This link illustrates this well. Keep in mind that a 3db loss is equivalent to roughly half the signal being lost.
Coax Cable Loss
In short, a wideband discone and wideband preamp are, in many cases, asking for trouble
HTH...Mike