That works, certainly worth a go outside and may be a really good answer for a tough room indoors. In the indoor case, point the cardioids at the PA speakers and the center hyper directly forward. Just make sure to space the cardioids far enough to make up for the pretty narrow angle between them (the improved PAS thing), and again more for introducing a third mic in the center. Off the cuff, I'd say use 2' minimum between the cardioids when used that way, and probably significantly more if you can swing it, but no sweat if not.
As a general rule, you want to put your more directional mic in the center, whatever it's actual pickup pattern, and use your less directional mic pair as the outer flanking pair. The other general rule is to use more spacing for three mics than you would normally use for two. You want at least twice the stereo pair spacing, if not more. Depending on the acoustic situation, you probably also want more angle between the microphones. Outdoors, if constrained to that same spacing used indoors, I'd point the flanking pair of cardioids directly sideways! Gasp! ..fully trusting the forward facing center mic, as a way to maximize the difference between the three channels and thus improving imaging, ambience, and minimizing potential phase cancellations. I point the omnis sideways too, which is perhaps less gasp inducing since they are omnis, because that increases signal difference at the highest frequencies where the omnis become directional, and usually also affords a few extra inches of omni spacing from a given bar length. Push 'em out as wide as you can get them.
If pointing two of the three mics sideways sounds radical, consider that 2 channel DIN is a 12" spacing with a 90 degree angle between cardioids. So in terms of the spacing/angle relationship, having the outside pair of cardioid facing directly sideways (180 degrees apart) with a total spacing of 2' and a third mic in the middle is pretty much the same spacing/angle relationship as two side-by side DIN setups sharing the center mic (doubled down double-DIN?). Outside, if I couldn't arrange to space omnis far enough, I'd do that as a way of leveraging the directionality of the cardioids to counter the limited amount of spacing I had available, otherwise I'd probably use choose omnis and space them apart more.
A single omni in the middle might be helpful if you have only one omni, or only one channel remaining, but I always prefer omnis in pairs spaced enough apart (for a couple reasons I'll be happy to go into if you like).
Ok, so sounds like I should should keep my ck61's in action because I really like their sound, and consider running split omni's (studio projects c4) and add a center shotgun. This way I can mix and match with what sounds best. In this case, I would only need to add a center shotgun or hyper card to my collection. Any suggestions on the center mic (i'm on a budget)?
You can also try the spit omni thing with one of your ck61 cardioids in the middle, before picking up a supercard, hypercard or shotgun. Or three cardioids in a row if you have a third. Simply having an array of three mics arranged in a row is going to get you a good deal of the way towards a more forwardly sensitive setup with center 'tunability' options which can be used to increase vocal clarity. It's sort of like an antenna array, and works even with three omnis, which is the way I did it outdoors for years before moving towards substituting increasingly directional mics in the center. Using a more directional mic in the center optimises things by tailoring the properties of each mic to the roll it plays in the combined array, isolating what the center mic picks up as much as is practical. But just having three mics in a line is a big step forward even by itself.
Since it sounds like you currently have both a pair of omnis (SP C4) and a pair of cardioids (AKG ck61), as well as a 4-channel recorder, I suggest you go ahead and take it one step further for your next outdoor event without having to buy any new mic(s) quite yet-
Setup the spaced C4 omnis as far apart as you can manage to get them, and the ck61 cardioid pair in the center as an X/Y pair rather than using just one ck61 facing directly forwards. Here's the important key for trying that- use a narrow X/Y angle. Pointing the X/Y cards at the stacks is probably your best bet, maybe even inside the stacks if not very far back when the X/Y angle might be greater than 90 degrees. You want a rather narrow X/Y angle because you don't want the combined X/Y pattern of the two cardioids to grow overly wide (remember, we want as much isolation as possible from extraneous sound arriving from all other directions as possible in the center, so as to not loose too much forward isolation), plus you will be getting most of your overall stereo information from the spaced omnis anyway. If you were only recording using one X/Y pair I'd argue for angling them something like 120 degrees apart. But in this case, a touch of stereo width from that still rather mono X/Y center mic position really helps blend the contribution of the center seamlessly with what the omnis (or spaced and widely angled cardioids) provide, and lends some really helpful psychoacoustic stereo ques to the resulting stereo mix.