More than 4 PWM output at 25khz?
Indeed you could use a Mega. See this answer: it explains how
you can use Timer&nbsp;1 on an Uno to provide two PWM channels at
25&nbsp;kHz. This is the only 16-bit timer on that board. The Mega, on
the other hand, has four 16-bit timers: Timers&nbsp;1, 3, 4 and 5. These
timers are almost identical to the Uno's Timer&nbsp;1, except that they
provide 3&nbsp;PWM channels each. So you have potentially up to
12&nbsp;PWM channels that you can run at 25&nbsp;kHz.

Now, look at this pinout diagram. Every pin labeled OCnx,
where n is either 1, 3, 4 or 5, and x is a letter, is a 16-bit PWM
output. Just take the code from the answer I linked to and adapt it to
the Mega. You configure all those timers in the same way, and you set
the duty cycle for pin OC3B by writing to the register OCR3B (and so
on...).