Thank you for the feedback. It seems you may be new to working with a DAW (my apologies if I misinterpret this), and there is a free 6-week course on Coursera by Berklee College of Music called "
Introduction to Music Production" that is full of useful information to anyone starting out. It is very well presented and not specific to any DAW, but loaded with advice. The next run is Apr 20 - Jun 14 and will not cost you a nickel other than your time (it is good to invest time in this if taking it).
Building up studio equipment often takes time, so it typically runs the cycle of buy something to resolve and issue, then find something new to resolve. I still have 1/8" to RCA Y splitters in boxes, so as soon as you mentioned hiss it made me think of the course above. I think we have all been down that path of working with what we have when starting out.
Going down your list, you actually have "drums" via the
Cakewalk TTS-1 and Studio Instruments Drum Kit. For "drums with no drummer" I would actually default to using the TTS-1, since it will do 15 other instruments for you as well. Granted it is not something you may leave in the final recording, but it fits the bill and you already own it (another no-cost one). The TTS-1, Step Sequencer, and Groove Clips included with MC6 are worth looking into.
From a recording (and even post-production/mixing) perspective, MC6 is very capable, so it seems your biggest "leap" is to get the cleanest signals (with least noise) recorded into MC6 in 24-bit format. I am not familiar with your specific hardware, but as long as you can get a clean capture you can work with it again at any time later. Conversely if the capture is terrible, all the mixing tools in the world may not be able to recover it.
Guitarhacker
Dedicated audio interface with nice preamps..... if the Alesis MultimixX4 4 channel usb mixer works well, this is something that you can put on a back shelf for the time being. As long as latency is manageable this could wait until later. I couldn't determine if the Alesis ran true ASIO or if it runs ASIO4ALL which is a wrapper for a less capable driver. Either way, if it works, let it stay for now.
From what you said, it "seems" this may be the most applicable (including good cabling). Headphone mixing is doable for short term, and can always be revisited later, but trying to mix something "unsalvageable" just leads to intense frustration.
I hope this helps some. Welcome to the forum! (I cannot see post count from my phone and just realized this when replying).