In terms of price-to-performance, I think the UcD modules are the best if you want more power than 100 W @ 4 ohms. Most implementations of class-D chip amps usually (realistically) top out at ~100 W @ 4 ohms.
If I understood you correctly, you are referring to the SMPS400A180 being out of stock, and the SMPS400A400 is in stock, right? If that is the case, the A400 output voltage (±62 V) is too high for the UcD180HG. You may want to switch to the UcD400HG instead. A single SMPS400A400 will be under power for two UcD400HG, but should work.
The UcD400HG amplifier module is a self-contained high-performance class D amplifier suited for many audio applications. Output power: 4Ω - 400W, 8Ω - 240W
www.diyclassd.com