I own a DB4e and am throughly impressed and satisfied with it's UHF capability. BUT... Antenna location is often the most important single factor. The right antenna, mounted in a location with poor signal conditions is going to fail to perform well. Have you tried alternate locations? No point spending more money until you have exhausted the possibility that there is a good location for the C2-V
As long as you are getting reliable reception with the VHF dipole of the C2-V ('reflector' per the AD marketing dept.
), I would suggest you stick with it. As long as you can work out a reliable mounting method for the dipole, it can be combined with any UHF antenna by simply using the UHF/VHF combiner.
The HDHR "Signal Quality" measurement is by far the most important parameter to optimize. "Signal Strength" is irrelevant if the signal is of poor quality.