I will appreciate any help in my endeavor to safely and correctly hook up the Rachael SE34I.5 as I try to make sure I don't do something wrong.

As it is now, it is a non-standard setup.  I am putting together the system, but it is a long ongoing process.  So now I have the Decware tube amp, the center speaker, and the subwoofer.

So, I think I understand that it isn't good to run the amp without being connected to speakers.  I think I understand that you can connect it in mono mode to a single speaker.  I am not sure how it works, but apparently it can be either "parallel" by connecting both + together and both - together, or "serial" by connecting the + of one side to the - of the other side, but I'd be pretty hesitant to do that as it just seems dangerous to a newbie like me, although the manual says that is the best way usually.

But then, for the powered active subwoofer, would I then just hook it up as it seems the manual recommends, with the RCA outupt jack even though there is only one speaker connected?  Is it OK to have a "1.1" system at least temporarily?  Or should I just wait to connect the subwoofer until I have a more proper setup?

Most active subs allow you to run speaker wire from your speakers to your subwoofer amp, allowing you not to have to connect the sub to the Rachael.

Looking at the Rachael manual, you have two options for bridging the amp to mono, the easiest way looks like this:

B) The left negative jack is connected to the right positive jack (series) and the remaining to unused posts will then be used to drive the loudspeaker.  Way B usually sounds better and requires a small 12 inch piece of wire to connect the two binding posts.

So you just need a small piece of unterminated speaker wire to connect left black to right red.  Then your unused speaker hookups go to your center channel.  Then connect your sub amp to your speaker using cheap speaker wire (if possible).

But if you're nervous about it, I'd just focus on the mono bridge to your center channel first and making sure it works, then focus on connecting the sub later.  Or call Steve and have him walk you through it, but I believe he builds the amps such that there's nothing you can do to harm them in terms of connections.

Many subwoofer manufacturers recommend you run your sub off your speakers instead of your preamp.  Sean at Zu told me to do that when I auditioned their Undertone sub.  The advantage is that the speakers and the sub both get the same amp signal and you don't have to worry if your preamp out is fixed or variable.  

The typical input impedance of speaker level inputs on a sub is very high, like 500 ohms, so high that the amp doesn't really see the load of the sub (the amp doesn't have to work any harder).

Wow Donnie, loaning me a couple of speakers would be spectacular!!!  It ALMOST makes me wish I was in Illinois, that is until I see the -3°!!!

I'm using the Klipsch R-112SW, and see that the inputs are RCA jacks.  Now, according to https://www.upscaleaudio.com/pages/subwoofer-tips, it really is a benefit to do this.

I'm thinking I understand whoopycat's information somewhat, that even daisy chained the sub still gets the signal it needs without needing to pull additional power from the amp (since it is powered itself).

So at some point I'll be trying this.

I do have another question before getting the Rachael going though.

From the turntable, there are three cables.  I can even figure out what they're for, and that two of them (RCA connectors) go to an input set on the Rachael.  But, the third is a spade connector grounding wire, and I've read the manual but don't know where there is a grounding lug or connector on it.  Another Decware manual for the ZP3 clearly shows what to do for that one.  "Once you are satisfied that all the tubes are hum and noise free you can connect your tonearm cables to the ZP3 and the ground wire from your turntable to the ground lug on the back of the ZP3."  Maybe it is completely obvious to people with knowledge about this, but I'm starting from the very beginning.