Center Channel Dilema

[Maggot]

A few years ago, when I got into Blu-ray, I gave my 70 year old parents my old Marantz receiver I had used in the days of DVD. I bought them a LCD screen and a Blu-ray player, so they can watch their DVD's unconverted and any future Blu-rays they might purchase. They are not interested in surround and are not picky about audio. They currently use my old late 80's classic Polk Audio RTA 11's for stereo. Much better than the TV speakers for sure, but they have noticed, as have I that it can be hard at times to hear dialog. Settings are fine and I am coming out optical as the Marantz receiver is pre-HDMI. I would like to get them a relatively cheap center channel to hopefully solve this issue. I've read comments left and right: Some say "absolutely, get a center channel to add to stereo", then others say "if you can't timbre match the center to your L/R stereo....it's better to have no center than something mismatched". Any thoughts? I was thinking of at least buying some current lower line Polk center channel to get somewhat close, but having not heard Polk's new stuff in 10+ years. Again, any thoughts?