Luxman M-700U vs M-900U

[Chewie]

I'm thinking of investing in a Luxman M-700U or M-900U stereo amp. If I went with the M-700U, I would possibly look to add a second a little later on and run them in monobloc mode. If I went with the 900U it'd be stereo only.

I've done all the usual searches and found one comparison, so I wondered if anyone here has compared the Luxman M-700U stereo amp to its bigger brother the M-900U? If so, are there pronounced differences in audio quality?

The latter is twice the price, and almost double the weight, so there must be some difference in sound quality, but can that gap be closed when comparing two 700's running in monobloc mode compared to a stereo 900?

Any advice would be most welcome!