In short, this is generally not permitted on HF. The G3RUH FSK proposal dealt with sending 9600 baud packet data over a 4800 hertz wide channel. The envisioned application was on VHF and UHF FM radios.
Many countries (including the US) restrict the data rates on HF frequencies to the equivalent bandwidth of an SSB voice channel or even less. SSB voice is typically considered to occupy a 2.4 kHz bandwidth.
The major data mode on HF in the last few years is called FT8. This mode is designed for weak signal communications and is optimized to exchange data needed to qualify as a confirmed contact. It occupies a 50 hertz bandwidth. There is a software suite of digital modes that includes FT8 called WSJT-X. The latest version is 2.0 with earlier versions depricated due to incompatibility. The success of FT8 is providing new insight into propagation conditions on HF.
In general, newer transceivers can be directly interfaced to a computer through a direct USB connection that presents the transceiver as both a USB sound card and, through a separate channel on the same USB connection, allows full control of the transceivers features.
Moving one generation back in HF radio technology, the rigs had a connection for rig control features (often through an RS-232 adapter) but did not emulate a sound card. To interface the sound channel to the computer, a special modem is used. A popular brand is RIGblaster.
Stepping yet another generation back, the HF radio will have no facility for computer controlling any of its features. The modem can still be used, however for data modes that can be used with manual rig control. Even FT8 is possible with this generation of radios although many of the desirable FT8 features cannot be used.
Your IC-9100 requires audio to be supplied via the ACC or DATA2 jack on the back of the radio. Either connection supports connecting to the PC speaker/mic or the use of a modem. In FM mode, you can run up to 9600 baud (if your regulations permit this) so 4800 baud would also work. See pages 171-173 of the English language manual for details. 4800 baud is considered "slow" data in this context. In VHF/UHF FM, AGC and transmit bandwidth are generally not a limiting factor. Do make sure, however, to turn off any equalizers, etc. to basically run the a wide, undistorted audio path in both directions.