Hi, and welcome to the forums! I can't explain everything in your post, but I woill start by saying if it were me, I would box up the Harmon Karden receiver and promptly return it to best buy. Harmon International owns HK, JBL, Infinity, Crown, and a few other companies. Not a big deal though, just FYI.
The Onkyo 605 is VERY VERY popular around here. Taken from Onkyo's website:
Processing Today’s High-Resolution Media—Including Blu-ray Disc and HD DVD—with Effortless Efficiency
Meet the first of Onkyo’s new A/V receivers built to embrace high-definition media such as Blu-ray Disc and HD DVD. The TX-SR605 7.1-channel A/V receiver embodies this new generation, with its remarkable processing capabilities courtesy of HDMI (High Definition Multimedia Interface). With the ability to keep everything in the digital domain, the TX-SR605 provides complete control of every video and audio format available today. Bringing high-definition A/V processing to Onkyo’s renowned approach to sound gives this A/V receiver a distinct advantage in the home. Delivering the latest in usability and versatility — such as multi-room playback, a full connectivity suite (with switching and upconversion), satellite radio connectivity, room calibration and integrated system control — the TX-SR605 is poised to set new benchmarks in performance-driven home theater.
Special Features
HDMI V1.3 repeater (2in/1out, 1080p compatible)
HDMI video up-conversion with DCDi technology
Dolby Digital Plus, Dolby TrueHD and DTS-HD decoding
One Call.com has it for 429.99 right now, USA model. GET ONE! It will drive your JBL's just fine.