One of the Axe-Fx's DSPs is more powerful than both DSPs combined in the Helix. Our tests show that the TigerSHARC DSP used in the Axe-Fx is over twice as fast as the DSP used in the Helix clock-for-clock . Now add that our DSP is clocked 50% higher the net power is about three times greater. So a single TigerSHARC is about 50% faster than both DSPs combined on the Helix. Yes, if we decided to use both DSPs for effects then you would be able to run more effects. 99% of our customers buy the unit for amp modeling so it doesn't make sense to invest the time and resources to making this possible.
Our algorithms are studio-quality and use more processing power than competing products. We've always been about quality over quantity. For example, our variable delay algorithm (chorus, flanger, etc.) uses poly-phase interpolation. EVERY competing product I have tested uses simple linear interpolation (or occasionally polynomial interpolation) which is far less computationally intensive but doesn't sound as good. This is demonstrable and measurable.
I highly doubt the Helix has two DSPs. My guess is that their claim of "blazing dual DSPs" is marketing for a DSP with two cores. My guess would be a Freescale Symphony (DSP5672x) DSP which is a dual-core DSP running at 200 or 250 MHz. While a dual-core DSP will be faster than the same DSP with a single core it will not have twice the power as the cores will share buses and contention for those buses will hamper peak throughput. The unit's capabilities are far below the Helix and Axe-Fx so I doubt their using a DSP with anywhere near the processing power. This is complete speculation though.