I think I'd tend to recommend getting a different soundbar, if at all possible, one with speaker-level binding post inputs.
A kludge for your current receiver would be a speaker-level output to line-level output converter plus an RCA to mini-jack adapter cable. (Both are readily available.)
Unfortunately, with that particular soundbar, I fear you'll need to spend a lot more on a compatible receiver than would be appropriate. The inputs on that soundbar model seem to be limited to line-level stereo (using a stereo minijack) and digital inputs with coax and optical connections. It's really intended to connect directly to a TV and to a disc player without an intermediate receiver. You would need to get a receiver which has either a digital output (coax or optical) or which has front left/right preamp outputs. The preamp outputs on your current receiver are only for rear-surround, height-surround or wide-surround connections to external amplifiers.
There are some receivers which have digital outputs, but they're older (no longer made) or top-of-the-line models which are getting a lot harder to find because of the migration to HDMI by modern equipment. Similarly, front left/right preamp outputs, analog monitor outputs or zone 2 analog outputs tend to be in more expensive receiver models, too.
To be honest, soundbars really aren't going to be able to produce a sufficiently high enough quality of sound that you'll be able to tell the difference between an analog connection and a digital one. That distinction can be quite difficult even with high-end audio equipment and speakers.
I hope this helps a little.
Marantz SR7009 avr + MM9000 amp --> Atmos 7.1.4
Fronts=NHT 2.9+AC2, FH+TM=DefTech PM1000, LCR+TM amped