You can only receive onemux per tuner, a single mux can havemultiple services.
An example.
Mux 666Mhz has 5 services, if the tuner can receive a full mux (most can now) you can view all services on 666Mhz at once.
If you wanted to view services on 698Mhz while continuing to stream services on 666Mhz, another tuner is required.