CMYK is more profitable than white ink anyway. My main DTG website has switched to white shirts only -- our profit margin went up almost instantly even though we "lost" 40% of our traffic on that site.
White ink isn't just tougher to maintain, it's tougher to print well AND tougher to get good artwork for. In June I know we wasted over 75 man-hours just dealing with crappy art for dark shirt prints. 75 man-hours x $40 overhead = $3000 of my money I threw away because the crap-for-brains "garment line" designers send 14kb JPGs for black shirt prints.
CMYK just needs a reasonably decent JPG and you're good to go.
I warn all my consulting customers NOT to do white ink for at least 3-6 months. Dial in CMYK, bang out dual CMYK jobs, and you can make $4-$6 profit PER SHIRT and print 20-40 shirts per hour with one guy, one printer, one heat press. That's $40-$150 per hour profit, more than enough to save up for a second DTG set up to test white ink out on.