Alot of people recommended me the same thing. The only thing im afraid of is killing the soundstage. The crystals sound amazing and get the job done, but just dont keep up. Im still conjuring up ideas so anyone is free to chime in.
I guess now that I've ranted I'll try and help you. First off, do yuo have phase controls on your sub amp? If so, play with your subs phase, you may find it blends much better, like night and day differenes in some cases. If not, switch the wires, a full 180 shift can still make an improvement. Also, try putting your mids out of phase. If you don't have a variable control on those, physically switch one side using the wires. Depending on the distance between your mids, you may end up with increased midbass. It's hard saying, but phasing is a no cost method to possibly fix your problem. If that doesn't work, try turning your LPF a little lower. If your using 80hz, try 60hz or something in that area. You may find it blends better with a lower crossover point. Subs that play high tend to overpower frontstages.
If none of that helps, are you sure you don't have room for a 3-way? You don't even need large drivers, use whatever size midbass you have in your doors as a dedicated midbass, a 3-4 inch midrange and some 1 inch tweeters would do fine. If you have ANY real kick space you can do a 4 inch mid. By freeing up the drivers you'll have a much better chance of getting the impact you need to keep up with the sub. An active setup would be a great idea as well, especially if you can fit a 3 way, then you can put the tweets higher up without hurting your staging. 3 way active FTW, IMO. If your doing a 3 way passive, I'd say keep the tweet in the kick if at all possible.
lasty, I strongly recommend AGAINST adding another set of components. If you have room to fit 2 sets of comps, you have room for a 3-way, which is 1000000x over a better option. Another set of components is going to give you MAJOR phasing issues, even if placed close together, it's just not worth it, unless all you care about is "decent" sound (read better than stock) with lots of volume, if that's your goal then it may work for you, this is all IMO.