It is possible for tuners used in different devices to have better or worse sensitivity when it comes to receiving channels. There are various signal scenarios that can change the performance of the tuner including signal strength, adjacent channels and multi-path (signal reflection) issues. When compared against the specifications of other tuners, the DVR+(CM-7500) is on par if not better than most. The tuner used in the DVR+(CM-7500) is of the highest quality manufactured by one of the top tuner manufacturers on the market. Specifications include a sensitivity of -87dBm (typical) and in addition taboo and adjacent channel rejection exceeding the ATSC A/74 specification.
If you are experiencing missing channels that another device will receive, this is not a defect in the product. As mentioned above, the two different tuners may be reacting differently because of the current state of the received signal. If you wish to view the missing channel it is recommended to improve your signal reception, including but not specifically to increasing/reducing signal strength, eliminating or reducing multi-path issues and avoiding EMI disturbances generated by common household appliances.
Please note: The tuner circuitry is set to be quite sensitive when trying to tune to 'poor Quality Signals'. There may be a time when your TV Tuner will allow a poor quality signal to be processed, but the DVR+ will reject that signal.