The autocom and starcom are just the bits that go on the bike, and that enable you to plug everything together so you can speak to your passenger, feed in music, phone and GPS voiice commands etc.....plus of course the walkie talkie of your choice.
The walkie talkie is the bit that needs to be compatable, nothing to do with the autocom/starcom.
Both systems will do the job you want...until the starcom came out, Autocom was the daddy, but apparently the starcom undercuts it pricewise- You'd need to do a search here for both to see the different views but either would suit your needs.
The walkie talkie, or more properly , the PMR446 device (446 mhz band ) is a more important choice...ideally you'll have the same models, but you'll need to check the details of the ones you both have if they're not the same, as although they should have the same basic channels, there are other tweaks that you might need to do to getthe radios to talk properly to eachother.
Check
HERE for a good article and starter on the info.
HTH