Analog or digital crossover for subwoofer integration?

IME, successful integration of a sub is vastly easier to achieve in the digital domain. If you use strictly digital source material, I'd say it's a no-brainer, go digital.  If you use analog source material, there may be  a philosophical issue with ADC and DAC in your signal path, so it's up to you and your philosophy.

By the way, IME room correction will help with the integration process  immensely.  Once you eliminate all of the FR ireegularities in the x-over region, getting a seamless hand-off is so much easier.  

As always, YMMV.

For the record, I did much the same as Bob, jettisoning ARC and Joule preamps for an Onkyo prepro.  I don't use active speakers because I prefer omnidirectional response ( and, AFAIK there are no active omnis).  You might consider flipping to NAD's two channel integrated that offers bass management and room correction.  You could also try to find a used (discontinued model) Harman Kardon HK 990, which is another 2 channel integrated with similar capabilities.

As to an analog crossover, the Marchands are hit and miss, mine was just too noisy.  You could try to find a used NHT X-1 or X-2 (also discontinued) which is an excellent, cost effective solution - if available.