Simultaneous Presentation with Multiple Stimulus Lists

I an still learning Superlab and am trying to figure out if there is a clean way to present two alternating screens using simultaneous presentations of stimuli taken from two different stimulus lists of different formats.

The alternating screens would be

(1) the “+” text and the string of letters " A B C D E F" above it with a dark patch in the lower left corner (that a diode can detect) and
(2) the “+” text and a vertical line directly beneath it " | " with a dark patch in the lower right corner.

These two screens have to flash very quickly (17 ms ideally) back and forth for about 5 seconds. (the five second interval is one trial; there need to be numerous trials)

I tried doing a stimulus list of pure JPEGs, but it is better to have Superlab draw the text portion because it is easier to manipulate placement font etc. I have JPEGs of the dark patches, but can’t figure out a way to do simultaneous presentations of the text and JPEGs to create these two alternating screens. Every way I have come up with creates significant lag or wont present all the components I have mentioned. Does anyone have any ideas or a direction they can point me in?

You can alternate the presentation of two JPEGs, or a JPEG plus a string of text, but I can’t think of a way to alternate the presentation of what you described.