Is this a change that needs to be be made with an internal soundcard or with an external one too?

I figured I'd post a follow-up to my own question: I called Cakewalk technical support on this and the guy was a bit stumped but suggested I try a few things, one of which was to use my other USB interface (didn't have it at home at the time) and see if the problem persists. I've run a couple tests using my TASCAM US-2000 and I don't hear any bleed coming from other inputs, so I'm going to chock this one up to a problem with the LAMBDA itself.

If it's any help to anyone struggling with a similar issue, while it didn't work for me for obvious reasons, the gents at Cakewalk recommended I right-click on Computer in the start menu and hit Properties, then go to where it says "Device Manager" on the side of the Properties window, and disable all the sound cards I wouldn't be using (in this case my computer's built-in sound cards). If you're struggling with a similar issue, give this a shot - of course you will have to re-enable these later to use your computer's normal sound card, but that's easy to do.

Put out a technical support request to Lambda. God knows what's wrong with this thing.

Welcome to the forum.
This is just an informational post and I think it's best to start your own thread in the main body of the forum. Just click the 'Post New Thread' button on the upper left.
Have you downloaded and installed the latest drivers and updates for the Juno? That looks like one complcated beast. Audio, MIDI, interface, controller and recorder in one package!