Question about multiple mid-range drivers

The Monitor 40 is a much better speaker than the Monitor 30. Go with the 40 for your fronts. They don't cost much more especially when on sale.

Use Monitor 30's or OWM 3 or 5 for your rear surrounds and the RTi28 for your side surrounds. Leave the Insignias out of the mix.

I would get the Monitor 40 speakers for the front and use the Rti28s to replace the Insignia speakers. The Monitor 40 speakers will do a much better job in that rather large room. Note that the Monitor 40s are rated to operate up to 250 watts of power and the Rti28 are only rated up to 125 watts.

The larger speakers can put out greater power with lower distortion; two 5" drivers in a larger enclosure move more air much more efficiently than one, in general.

Also, the Rti28 speakers are really only fully effective down to about 70 Hz; Front speakers for a room like you have really should be able to go down to around 50 Hz for proper multi-channel mid-bass sound, and the Monitor 40 speakers will do that. When you say that bass response is not an issue you are 100% wrong.

Remember that a subwoofer is MONAURAL, and is no substitute for having front speakers that go fairly low and using them fully. The subwoofer is there ONLY to produce the lowest frequencies that your front speakers CAN NOT put out. Why have 5 speakers and then allow a significant part of the sound to be monaural when it should be stereo? How much sense does that make?

I think that you will find that the Monitor 40s will be a great improvement, and that the bass they put out will be make the sound much better in the room. Having the larger front speakers to produce that critical mid-bass from 50 to 70 Hz will be a huge improvement in the way your system sounds IMO. I have seen this kind of change totally transform a system over and over. Front speakers that are too small are a big problem that too often goes unrecognized, and it is certainly the problem in your case.

Check your receiver manual and see if it allows you to set per speaker crossover or one setting for all. If the latter, then note the OWM3s are rated down to 80hz. It's possible that they'll really need a little bit higher crossover than that just for them, essentially limiting the entire setup. In that situation, the Rti28s make more sense. You should be able to set the crossover at 80hz for all your speakers with them as the rears.