Does It Hurt....

No it should be fine. 

Nope, not a problem. I did that myself for a while when slowly switching back from a 5.1 to a pure 2 channel.

In theory, whatever capacitors and other parts in the unused channels may atrophy from disuse

more botness.

Thank you for taking the time to answer this question!!

It doesn't hurt the unused channels, but their self esteem does take a beating.

No one likes to feel like their existence is meaningless.

@tony1954 *L*  The idled amps in my multichannel bitch daily 'bout just that....*sigh*

I threaten them with a 'dummy load'...that seems to mollify them enough for awhile...

If you are not going to use the redundant channels you would do better selling the receiver and getting a proper two channel amp.

@yoyoyaya 

"If you are not going to use the redundant channels you would do better selling the receiver and getting a proper two channel amp."

Not really. I am in the same situation, with my Anthem AVR only used to power my centre channel and one subwoofer. But, more importantly, it serves as a hub for outputting the L and R channels to the HT Bypass on a Musical Fidelity M6si and it allows for connection of all my HT components via HDMI. Something a "proper" two channel amp wouldn't be capable of doing.

What's hurting you more is using an AVR in a 2.1 system.  The compromises made in order to get all that processing and all those channels into one box doesn't leave much for fidelity.

Thanks for the responses!

All I really need is something that I can run my sound from my TV to my JBL bookshelf speakers without breaking the bank. 

@op - if that's the use for the amp, then you are fine as you are. In fact, chances are that your receiver's power amp sections share the same power supply. That being the case, if you are only loading two of the channels, those channels will probably perform the better for there not being other speakers connected.

yoyoyaya

Thanks for that response!