4, KCNC CBS, virtual channel 4.1, real channel 35, NM 5.9 dB
http://www.tvfool.com/?option=com_wr...dALLTV%26n%3d8
7, KMGH ABC, virtual channel 7.1, real channel 7, NM 21.9 dB
http://www.tvfool.com/?option=com_wr...dALLTV%26n%3d4
9, KUSA NBC, virtual channel 9.1, real channel 9, NM 19.1 dB
http://www.tvfool.com/?option=com_wr...dALLTV%26n%3d5
31, KDVR Fox, virtual channel 31.1, real channel 32, NM -6.6 dB
Notice that only 58 of 1000 kW ERP is sent in your direction because of the transmitting antenna pattern
http://www.tvfool.com/?option=com_wr...ALLTV%26n%3d12
I doubt that another preamp will improve your reception, unless the RCA preamp is defective.
You might be able to improve the reception of 7 and 9 if you replace the RCA antenna with an MCM 30-2476
http://www.mcmelectronics.com/produc...-2476-/30-2476
If your Dual Quad Bay Outdoor HDTV/DTV/UHF Bowtie isn't able to receive the local UHF channels with both panels aimed in the same direction, I doubt that any other UHF antenna will. A longshot replacement would be an Antennas Direct 91XG because it has a tilt adjustment that would allow you to tilt the front end up to better catch the signals as they come over the ridge.
An extreme solution would be a pair of 91XGs side-by-side:
http://www.aa6g.org/DTV/index.html