Lelik

As the other guys already told you, you do not need any other device. I also prefer some "external" IRs instead of the Helix stock cabs. But it means only that you have to find them (some free ones, but many good ones are available for little money, and they are worth it), and with the software connecting your PC to Helix, you just import these IR files into the Helix. IRs are just small wave files giving you the typical frequency response of some specific speaker + mic.

If you just want to mix 2 IRs you can use a simple and free wave editor like Audacity. I explained here how to do it: https://www.thegearpage.net/board/index.php?threads/why-not-mix-your-own-customized-irs.1808660/#post-23778431

I have the latest firmware 2.21. By mistake I assigned 2 things to a switch: two different channel volumes of an amp sim, and also the bypass of the same amp sim (that I did not intend to assign at all). I don't understand how I can clear these assignments (both and/or each of them). Could you help me please? I tried to find this information in the manual (the only one I found is for fw 2.10) but I can't understand it, or there is some different behaviour in the current fw. Thanks!