If you own the RS750's then I highly recommend upgrading the crossovers. It will take those speakers to another level of performance and make them very enjoyable to listen to.
They are not however, on the same performance level as an OB-5 or OB-7. Those are very different by design and are an apples and oranges comparison. The OB-7 uses a planar magnetic tweeter crossed low to open baffle mounted midbass woofers, multiple lower end woofers and a powered 12" sub. Fully assembled the OB series speakers would also be considerably more expensive than the RS750.