Do the ES20 speakers need an amplifier?

Yes. They are passive speakers with no built-in amp, so you need a receiver or power amplifier. Any stereo or AV receiver rated around 20 to 150 watts per channel will drive them.

Do they come as a pair?

Yes, they are sold as a matched pair. Speaker wire and stands are not included.

Can I use them as home theater surrounds?

Yes. They work as front left/right or surrounds in a multichannel setup. Their size suits surround duty, though wall mounting needs brackets rated for their weight.

How do they compare with the ELAC Debut 2.0 B6.2?

Both are neutral two-way bookshelves with 6.5-inch woofers. The Polk is often described as slightly more forgiving and wider-dispersing; the ELAC is often called a touch warmer. Either suits a receiver-based stereo or theater system.

Do they need a subwoofer?

For most music, no. For movies and deep bass, a subwoofer fills in below their reach and lets you cross them over higher for cleaner output.

Where should I place them?

Put them on stands or a shelf at ear height, angled toward the listening seat, and leave some space behind the rear port. Close-to-wall placement thickens the bass.