All 16 channels require the FrSky Taranis, or the XJT module. For 8 channels in D8 Mode you can use the FrSky Taranis.
The X8R is in a Smaller package then previous 8 channel receivers, but has so much more capability. The new Smart Port supports the new hub-less sensors as well as the older hub analog sensors.
The X8R supports 8 standard servo outputs, and you can access all 16 channels by using the Sbus line with Sbus supported servos or use a FrSky S.BUS Decoder for the full 16 channels. Or you can use 2 X8R receivers in combination and the channels will sync 1-8 on the first and 9-16 on the second.
Specification: Dimension: 46.5mm x 27mm x 14.4mm (1.83″ x 1.06″ x .56″) Weight: 16.8g (.59 oz) Operating Voltage Range: 4V-10.0V Operating Current: 100mA@5V Operating Range: >1.5km (Full Range) RSSI output: analog voltage output (0~3.3V)