Sorry if you’ve covered this before but can you explain a little about what you are trying to achieve? I can only assume that you feel the M1 integrated is not driving the FR-5’s well (enough)?
In very general terms, bi-amping reduces the load placed on each ‘leg’ of the amplifier by the speaker. So in theory, the amp has slightly more headroom than would otherwise be the case. Whether you perceive this as an ‘upgrade’ or not might be debatable as results from bi-amping seem to vary.
I have no direct experience of bi-amping with Roksan kit but I used to run a bi-amped Meridian set up. With respect, I think you’d be heading down a blind alley by purchasing either of the amps you mention and running them with your current integrated amp. The FR-5’s are pretty demanding and I’d go with using monoblocs instead and when funds allow swapping out the integrated for a dedicated pre-amp. That is actually where I experienced the biggest gain in my old set up.
You may be looking for an ‘easy’ upgrade but if I were you I’d be saving for longer and getting the pre/mono’s in one go.