Parents need clear sounding 2 ch HT

I think your parents are suffering hearing issues that seem to them as garbled sounds but is really a medical matter. They probably need the speakers near to them and the volume on the louder side for them to be satisfied. I would advise them to get their hearing tested. Then other options aside from what I suggested may be appropriate.

Room treatments will reduce reverberation and improve clarity. When I bought acoustic panels warehouse clerk showed me conference room that they treated 100% with acoustic fiberglass foam (floor to ceiling between studs). Sound was amazing. I've never heard another person speaking with such clarity, sound coming directly from his mouth. It was amazing. Perhaps it is not good for music, being over-damped, but is perfect for clarity.

Further to Kal's comment, I' d add another step (if they're using an AVR).

Add a center channel, use the auto set-up on your AVR and then manually increase the volume level of the center channel. This problem is often a result of effects being mixed very loud relative to dialogue in an effort to maximize the sonic impact of the audio.

Bumping the level of the center channel may reduce some of that impact, but IME It will usually help make the dialog much easier to hear.

Good Luck

Marty

If they can't understand what was said on tv, then it's the midrange that needs to be more pronounced. Usually you can do this on a receiver by rolling off the bass and maybe accentuating the treble a bit. Adding a center channel may also help, but I think the key is turning down the bass.