I don't think the tips are going to cause resonance; if anything they help mellow out the tone. I have 4" tips that're 18" long on my truck and it sounds a lot mellower than trucks without tips. I used to have true duals with straight pipes with these tips and the resonance wasn't bad at all considering how loud it was. I think some short mufflers like Dynomax bullets or something of the like will help you out tremendously.

 

Yes I am catless.