Thanks for all the replies - sorry for not specifying what I'm using; Windows 11 and Sonar.
I have absolutely no issue continuing to use the Line 6 in the way it's intended, I was just trying to mainly get around the vocal issue. I was recording some guitar last night and it's very easy to get the dry/wet signal recorded simultaneously with very little effort, and the Beringer certainly sounds no better, quality wise, so it's not a case of that either.
Vocals are the only main issue - I'm unsure how one would have two different interfaces connected at the same time, since Sonar (quite rightly) prevents them both being enabled at the same time. Is it a case of having to go into the audio settings every time you want to switch them around? Not ideal, but not terrible...
For Vocals, I've also seen suggestions for using something like this:
https://www.amazon.co.uk/Audix-T50K-Adaptateur-Impédance/dp/B0018STX4C/?_encoding=UTF8&pd_rd_w=FxzRs&content-id=amzn1.sym.ef3907ff-f91d-4263-9e4a-2471c52bf60e&pf_rd_p=ef3907ff-f91d-4263-9e4a-2471c52bf60e&pf_rd_r=21YV5YJM6C84P8ZBTH6N&pd_rd_wg=nf9FZ&pd_rd_r=5e4e1f2a-6e14-4afd-aaa6-2a2fa7e4911b&ref_=pd_gw_ci_mcx_mr_hp_atf_m
Not sure exactly what the results would be, but the cable isn't cheap itself so cautious before just randomly picking one up.