Thanks Arnold for the reply.
This is the speaker specs.
System type: 2.5-way, rear ported
HF driver: Morel 28mm soft dome
Bass/mid driver: Morel 14cm DPC cone
Bass driver: Morel 14cm DPC cone
Room response: 40Hz-22kHz
Sensitivity: 89dB/1 watt
Power rating: 140 watts
Impedance: 6 ohms nominal
Crossover: 280Hz and 2800Hz
Dimensions(cm): 87 x 16 x 22 (h x w x d)
I have noticed a big difference when they are bi-amped using the front and rear terminals, to me it sounds like the RX-A710 may be lacking some current - I believe the Yammy is 35amps vs the HK at 80 amps.
Its not bass that is the problem but rather a slight distortion as songs like Porcupine Tree - Even Less and Acoustic Alchemy - Mr Chow for example has very deep bass guitar and it handles that rather well, it seems to be a problem when I am playing hard rock where things are a little more cluttered as in a couple of lead guitars, male vocals, bass guitar, rhythm guitar and drums etc all happening at once that I notice it to be lacking punch almost as if I'm pushing the amp to its limits at mid volumes where as at low volumes it sounds ok.
It to me appears in the upper bass - lower mids where it is lacking or possibly distorting.
I do have a 10" sub (Polk Audio PSW110))