tl;dr
" really do not want to have to go into each song and readjust levels and the entire mixes to even everything out"
You’re probably going to have to do this. Meter well, stay green and apply a consistent pattern to how you use volumes … read more about what I did below 
Hi, I play live using both these boxes, and the problem of levels took some thought.
When I started with the AR2 I just jumped straight in. I created some really usable patterns, but I had no idea how the volumes worked. This was quite a mess!
I can tell you what I ended up with, which I consider to be a success.
First up, I run everything through a Tascam Model:16 mixer and on that I have a master volume meter. I have sticky labels on that which mark a set level (0db). The labels are clear enough to be seen from acute angles or from distance, meaning that I can always use the level meter consistently regardless of where things are set up. The mixer channel, which takes a single source out of the OT is flat, gain at 0, no compression, no FX, and flat EQ.
I then use Beyer Dynamic DT1990s with the analytic pads so that the reproduction of the output as sound waves is also as flat as possible.
This means that I can level my live setup as close as possible to flat, then when it’s taken out live, where I use monitors and whatever mixer the PA uses I can be as confident as possible when I plug in.
In the OT I set up two channels for two Rytms, each which ends with a compressor. I send a green signal with all elements from sub to high treble playing into the OT then use the compressor gain and AMP pages to boost the volume to the point where it fills the mixer output up to my mixer labels. With the mixer output I check that the last light before the label is on clearly, but not solid, it should be full, but not leaking into the next level. There’s usually quite a bit between a light just flickering with the peaks and a light being solid and I’m aiming for the mid point pretty much. This precision is important.
It’s also useful to know what level of lights are created by different elements. For example, kicks played on their own are likely to flick the top light on clearly, whereas hi-hats on their own might only light up the lowest of the lights below the label.
I then haven’t touched this, I just push everything up to this limit carefully, and it matches the flat, 0db output of the mixer. Note that if something is too loud you should be able to see it in the OT input meter as orange then see the same peak in the mixer (and hear it too).
In the Rytm there’s a number of volumes to choose from, so I’ll list them here and describe how I use them. The goal here really is consistency, you want to be doing the same thing across patterns with the different volumes. I find this method works well and enables me to consistently refine the levels of a pattern, be that the master level, or LFO, or track level, etc.
Compressor: I don’t use this in the Rytm. I could do for creative purposes but not for levelling.
Compressor page master level: this I set to 100. Keeping this consistent across patterns avoids one output completely swamping the other and means the balance of FX level is easier to manage (this level does not control FX level, turning it to 0 leaves just the FX wet playing)
Track level: all set to 100.
Amp page track level: this is what I use to balance the level of the track. By manipulating these across all my tracks I can push everything up into the mix so it’s clear while monitoring the lights on the mixer to make sure I don’t push anything too far. I tend to change these only with the full track playing. This is also the focus on the LFO for volume LFO gate tricks. Never higher than 110.
Machine page and sample page levels: These two are used to mix the machine with the sample. Their function is sound design. It’s not unusual to have the machine on 100 and the sample on 10.
Velocity: this is where volume differences across steps are programmed.
All this means I can quickly adjust volumes for creative reasons, frees up sound design possibilities, allows me to mix tracks, and provides me with a clearly defined ceiling to push up against which is always green.
And when I’ve played live, which I have only recently started to do it has been successful, there’s not been much need for processing in the PA (a bit of bass boost) or for an engineer to be monitoring my playing and making adjustments. And folk stayed and danced.