If it just the selector unit you might be able to get it back by chaining the ink selector/damper assembly.
First, don't dilute the M/C and LM/LC inks the same just so you can use the Epson driver. It is a waste of a multi-channel gray ink printer. Also, if you do want to use it with QTR and those dilutions you'll miss out on what you can do with the partitioned inks. You could still partition them with different ink limits, but they might be a little wonky because the limits will cause one to print lighter and you might get dots, or weird bronzing when making gloss prints.
Here is what I would actually recommend. Get the Piezography Carbon Inks with the HD MK and PK shade 1 and protective spray or gloss overprint for MK/PK compatibility (getting Piezography inks because they better/more reliable/easier than diluting yourself).
I would set them up in this order.
ML/PK - broken... throw in some expired epson carts...
C - Shade 2
Lc - LC (oem/refillable color ink)
M - Shade 3 (or Shade 4 if using Gloss overprint — shade 3 is not needed if using gloss overprint)
Lm - LM (oem/refillable color ink)
Y - Shade 4 (or shade 5 if using Gloss Overprint)
Lk - Shade 5 (or shade 6 if using Gloss Overprint)
Llk - Shade 6 or Gloss Overprint
Or - Pk
Gr Mk
Then get my QuadToneProfiler-Pro system and then an i1 Pro off ebay so you can measure in scanning mode (all the ink limits and partitioning is done automatically from two calibration targets).
The new tools have my own partitioning formula that will not require you to use the toning curves to hide the partitioning points (the only reason you might need to use the toner curves to hide the partitioning points is because they were not set correctly in the first place). My partitioning system makes smoother curves than the traditional QTR curve creation formulas with more overlap of each neighboring shade and smoothing start and stop points.
With that system you will be able to use any number of inks—like all carbon and then use my new gray balance tool with the Lc and Lm inks for toning. You won't be able to make a "cold-toned" print but you can easily neutralize the warmth or make a warm selenium-tone and then do a range of split tones with the QTR curve blending.
Take a look here: https://www.bwmastery.com/quadtoneprofiler-pro/