I entered your zip code at antennaweb, just to see what came up.
* yellow - uhf KTVI-DT 2.1 FOX St. Louis MO 261° 25.2 43
* yellow - uhf KMOV-DT 4.1 CBS ST. LOUIS MO 259° 21.4 56
* yellow - uhf KDNL-DT 30.1 ABC ST. LOUIS MO 268° 22.6 31
* yellow - uhf KSDK-DT 5.1 NBC ST. LOUIS MO 266° 22.7 35
* yellow - uhf WPXS-DT 21 IND MOUNT VERNON IL TBD 98° 23.4 21
* blue - uhf WSIU-DT 8.1 PBS CARBONDALE IL 133° 49.5 40
* blue - uhf KETC-DT 9.1 PBS ST. LOUIS MO 254° 27.3 39
* blue - uhf KNLC-DT 24.1 FMN ST. LOUIS MO 246° 38.0 14
* blue - uhf KPLR-DT 11.1 CW ST. LOUIS MO 267° 22.4 26
* violet - uhf WRBU-DT 46.1 MNT E. ST. LOUIS IL 246° 34.2 47
Note:
Antennaweb is notoriously pessimistic when it comes to digital station reception; based on these numbers the CM4221 would certainly get the four network stations and probably the other St Louis stations as well , depending on how much attenuation is introduced by your attic. If it's one of those with metallic-lined insulation in the attic roof, predictions are very difficult to make. The CM4228 would just be, well, better. It is basically two CM4221's. It's more expensive of course, and you may have to dismantle it, as we discussed. But you have to aim it more carefully because it has a narrower beamwidth than the CM4221. And as has been mentioned, attic installations can sometimes create multipath which is a major problem for digital signals.
Preamps are used to overcome cable losses and also the effect of splitters, so you may not need one unless you have a very long cable run or you are splitting the signal to multiple TVs. The CM7777 is an excellent preamp where you do not have very close in stations which can cause overload.
