Accuphase pairs very very well with Focal Utopia Be speakers. You do not need to go to their separates to best your current Musical Fidelity integrated and you have quite a few choices (e.g. even the old E-406 and E-407 integrated are supperior to the Tri-Vista 300, while the newer iterations E-408, E-450 and E-460 even more so).
However, if funds permit, the Altos really deserve separates. My recommendation would be one of the Accuphase "mid-class" preamps (C-2400, C-2410, C-2800, C-2810) with an Accuphase class A power amp (e.g. A-50, A-45, A-46, A-60, A-65). The Accuphase class A amps do not get nowhere near as hot as similar designs from Pass Labs for example. However, if they still get too hot for you, Accuphase have very many A/B amps that sound very similar to their class A designs.
Having said all this, I should also say that your Trivista 300 integrated also pairs very well with the Altos. Thus, proceed with care and sell your MF integrated only after you are 100 percent sure you like the new-electronics-Alto combination better.
Good luck and keep us posted!
Paul