Before suggesting microphone setup ideas, let me ask a question-
Are you comfortably adept with not just time-aligning the starting points of the files recorded on two seperate machines, but also time-syncing one file-set to the other when necessary? This involves precisely time-stretching or time-shrinking the files made on one recorder to match time-points of the files made on the other, and becomes necessary for recordings of significant length when the clocks of the two recorders are set to run at the same nominal sampling rate, yet in reality run at ever-so-slightly different speeds. It is a practical issue of correcting for clock tolerances and the most complicated part of recording multichannel across more than one recorder. If you are good with doing that, we can provide good suggestions for the use of more than 4 channels. If not we can still recommend 4 channel options for recording into the R-44 on its own.
The way I look at it myself is this- I'll make the effort to time-stretch in a few cases, but most of the time I'll try to record everything onto one machine whenever possible. It just makes everything smoother, easier, and more enjoyable - from making the recording, to maintaining and cataloging your SD cards and files, to mixing the recordings.
What are the exceptions?
1) Figuring it out- Determining what techniques work for you and if recording more than 4 channels is worth the effort or not. This may take a while, which is fine as long as you are okay with doing the sync work. If you do decide it is worth the effort, I'd suggest moving to a 6-channel recorder sooner than later. That will make everything more straight forward, and can even potentially sound better as well with all channels always in phase-synch down to sample level. You can pick up a Tascam DR-680MK2 quite inexpensively these days, which will allow you to record 6 channels onto one machine (up to 8 channels if using it's digital coax input simultaneously). There are other 6-channel recorder options but, along with the R-44, the DR-680 is my favorite multichannel "taper" recorder. You may never need any additional channels than the 680 offers, but you'd also gain the capability of sharing clock between the DR-680 and R-44 so that you could record up to 10 channels using a single shared clock (which you cannot do with most other currently popular 6 and 8 channel recorders). The files from the two separate recorders would need alignment to the same initial start-point, but once aligned will stay in sync with sample-accuracy and no time-stretching/shrinking needed. I recognize that you specifically listed the equipment you have on hand, so I'll stop talking about a new recorder, but just keep in mind this dynamic if you decide to press ahead long term with recording more than four channels total.
2) Getting a SBD recording, either when SBD is available via USB, or if my primary recording location is not adjacent to the soundboard.