I'm afraid I've already given the best solution I can think of in THIS POST. I'll post it here again, tweaked to do exactly what I'm 74% sure you want:
X- Keys - Hold Alt.kmmacros (23 KB)
X- Keys - Press Tab.kmmacros (20 KB)
All you have to do is replace the Stream Deck triggers with your X-Keys ones.
Again, the drawback is that, because it uses AppleScript, you have to wait about 0.5sec before pressing the second key. This is the best I can do, I'm afraid.