I will be going to THT, possibly today to audition the SR 6300. To be sure if this model would be a worthy upgrade. Just to expand my options besides HK 3550. If no significant diffrence in the musicality of the 4300 and 6300, besides the power, then 3550 will be my only option for now. But I have yet to hear the 3550, I only heard the 5500 so far.
But if I have the money for the 5500, I think I would rather buy a separate audio amp, and stick with my 4300 for ht. It's really for audio listening that I'm planning to upgrade.