Another Question About Surrounds

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Hi everyone..

Im new here and new to this home theater stuff.

Ive got my first home theater set up using an onkyo 705 with 5.1 polk monitor series - c2 center, monitor 50 for l/r fronts and monitor 30 for side surrounds. My buddy is upgrading his speakers and offered to give me his klipsch synergy s-1 surrounds. So my questions is - can mix or the monitor 30s with the s-1s for surrounds or will the klipsch not mix with the polk.

If they can which would anyone recommend for sides and which for rears.

If you dont suggest mixing then i can let him know to give the s-1s to my other buddy.

thanks!