After reading in this thread - http://www.vintage-computer.com/vcforum/showthread.php?40965-Commodore-128-Video-DAC-Board-Available - that the DAC board would work, in conjunction with the GBS-8220, with PC CGA, I ordered one from http://he-insanity.blogspot.com/2014/03/commodore-128-cga-video-dac-board.html
It works! On my $20 thrift store HP flatscreen @1024x768, the colors are good (my camera washes out the lighter colors):



The characters are crisp, much more readable than the standard jr monitor, although some pixels are grey instead of white:

Additional items needed:
1) Adapter cable for IBM color display
2) DB-9 M/F extension cable (I got a 6' cable cheaply at a Tandy store close-out)
3) A 5VDC power supply, 5mm-2mm
4) 1 6-pin Molex connector (Digi-key numbers on the DAC website) to adapt the GBS-8220 cable to the DAC adapter
5) 2 2-pin Molex connectors (Digi-key numbers on the DAC website) to power the DAC from the 8220
Mike
*Manual: http://www.jammaboards.com/arcade_manuals/GBS-8220_CGA_to_VGA_HD-Converter.pdf
eBay source: http://www.ebay.com/itm/261153377967?_trksid=p2060353.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT