Best ARC Solid State power to match ARC Ref 5 Pre

ARC SS amps stand on the same level as Classe, Mccormack.
McCormack has the best performance for the budget.

I'd recommend the ARC HD220. This is a hybrid and sounds simply wonderful. Plenty of power too.

forgot to mention ARC 100.2 runs HOT so it requires plenty of ventilation

I would recomend either the HD220 or M2.2 mono blocks if you have the extra coin.

ARC's preamps can be very, very good, but their amps are quite overrated in my opinion - they all use copious amounts of global feedback, whether tube or solid-state, and while generally transparent and resolving, feature the closed-in dead quality and two-dimensionality that amps using feedback suffer from. In addition, many of their pentode-based tube amps cut corners in ways that are inexcusable given their price, such as the lack of individual biasing for tube pairs. In any event, stay as far away as possible from ARC's digital amps with Wilsons - I know a fellow with a new ARC digital amp (I think it's the DS225) and Sophias and it is exactly as I would have expected - that Focal tweeter with a digital amp is just awful.

No-global-feedback amps, such as darTZeel or Ayre, tend to be very expensive. If they are beyond your budget, I would look at the Rowland Model 2/6/8/9 series, which can be had for very reasonable prices on the used market. Like ARC gear, they are fully differential balanced. I agree that the Lamm solid-state amps are very fine, but they are quite expensive, even used, and the Class A-biased model runs really hot. Both Lamm and Rowland work well with Wilson, especially Lamm (Wilson and Lamm have frequently shown together at CES's).

I have a friend with a Ref 5 - it's a really fine preamp once broken in.