The number of wireless communication devices has grown exponentially with the evolution of wireless systems. Moreover, the development of technologies such as the Internet of things (IoT) and massive machine-type communications (mMTC) are also fueling the rapid increase in the number of communication devices. It is anticipated that through 6G, the wireless communication networks will move in the direction of ultra-dense distribution of enormous devices with assorted service and rate requirements. This requires a huge network energy, capacity, and efficient deployment of the spectrum. This paper employs the massive multi-input multi-output (mMIMO) and non-orthogonal multiple access (NOMA) techniques that increase the multiplexing gain and network capacity. This paper utilizes the benefits of millimeter Wave (mmWave) and Terahertz (THz) channels that poseess considerably higher communication capacity. However, these schemes are highly complex. To mitigate this problem, we use BS caching as diverse applications in 6G will have varied rate requirements. In addition, we propose an application-specific channel selection (ASCS) scheme with a cache-enabled two-tier 6G Heterogeneous Network (HetNet). In the proposed scheme, bestowing to the application requirement of the small cell users, the small cell base station (SBS) switches downlink channels dynamically. The simulation results illustrate that the proposed ASCS scheme can achieve higher spectral efficiency, energy efficiency, and throughput for the cache-enabled two-tier 6G HetNet.