For quite some time now, I’ve cobbled together a makeshift SEND command for the various amplifiers I’m using with an Icom IC-9100. Essentially, I just plugged together all the PTT lines and let it go at that. I’ve also used the DX Engineering Keyline 3 to protect all the lines.
I’ve finally built a connection box and cables that use the IC-9100’s Accessory Socket to trigger an HF/6 amp and a VHF amp separately. It uses pin 3 for HSEND and pin 7 for VSEND. Those, along with the 13.8 VDC provided by pin 8, are used to actuate a relay that enables the appropriate amplifier. You can see the Icom recommended circuit diagram below.
I found Potter & Brumfield 12 VDC SPST T90S1D42-12 relays on eBay. I also found a handy box to house the circuit and some phono jacks. You can see my handiwork in the photo below. One side of the box is the cables to the rig; the other is the cables to the amplifiers. In my case, the 6-meter amplifier is a TE Systems unit and the 2-meter amplifier is an RF Concepts unit. 
It’s nice to have a project come together and actually work. My next consideration is how to use an ALC voltage to provide different power levels for the two separate amplifiers. It can be done as a few have advised me they use an Arduino for the task. Something to consider.
Good luck in your ham radio adventures.
[…] downside is that IC-7100 does not have a separate PTT connection for an amplifier. But you can implement that with the ACC connector, including separate HF/6 and VHF/UHF PTT lines. That could be useful if I return to VHF roving or […]