The T-G10 is Onkyo's ultimate high-end FM tuner, as were the DX-G10 that brand's penultimate CD effort (until the ultimate C-1E) and the A-G10 (until the ultimate A-1E).
In other words, Onkyo put everything in it, everything they knew and could do...
However, the T-G10 / T-9090II is only a 1988 update on the previous T-9090 from 1984 - maybe the Onkyo engineers thought that finally not much could be added to (their) high-end FM reception ?
The T-G10 was a US-only version and seems (seems ?) to not have been available in its home country, Japan ; it however saw versions in Europe as T-9900 (aka T-9090) and T-9990 (aka T-9090II).
First is SFR, Sonic filtering Reception, which is a way to keep the VCO output unaffected by external vibrations such as sound pressure waves from the loudspeakers. These (possible) vibrations, or temperature-related frequency drift, can generate distorion in the high-frequency output of said VCO.
Sadly, conventional PLL (phase locked loop) cannot maintain VCO output accuracy in the tuning range and the resulting inaccuracies result in slight tuning errors... and distortion.
Onkyo's SFR is a dual-mode PLL circuit : one PLL works at fast response during tuning, and another to a rate more appropriate to natural musical reproduction once a broadcasting station has been selected.
Next comes APR, Automatic Precision Reception, which automatically chooses the better signal coming out of either antenna inputs - cable or air waves. APR can be switched manually as well - which is highly recommended.
Ok, that was SFR and APR.
Now for the real meat : copper front-end shielded case, five pure copper bus ground lines, shielded casings for the digital and power supply blocks, and a damping steel base panel to prevent mechanical vibrations and possible microphony.
Also a power supply filter and 25Khz fine-tune steps and all the possible station memory modes, timer modes, multi-function display, preset scan, auto-memory, IR remote-controlled output volume for the variable output etc. And wide / narrow / super-narrow modes, high-blend, RF modes, IF modes - did I leave anything out ?
Oh - yes : the real wood black piano sideburns !
As for the other separates in the series (A-G10, DX-G10, P-308, M-508) the T-G10 sports a Grand Integra badge while the rest of the world saw them with only Integra - and not even a badge...
I for one prefer my bigga Sony ST-A7B but we all have different ears and preferences :)