Cross correlate a 2D array
What you have (conceptually) is not a 2D array but a collection of 1D arrays. correlate2D is designed to perform a 2D correlation calculation, so that's not what you need.
Iterating through all pairs is not a big ask really - you can still use numpy to perform the cross correlation, you'll just need to have two loops (nested) to determine which signals to perform the calculation on. With only 64 signals that shouldn't take long.

for first in range(n_signals):
    for second in range(first + 1, n_signals):
        corr = numpy.correlate(data[first], data[second], mode='full')
        max_corr[first, second] = numpy.max(corr)