Bigger Impact

So I’m in the mood to buy something. What would have a bigger impact on my drum sound, getting 3 of the new Sennheiser mini 421s for my toms or switching my interface setup to an Apollo? I currently have the focusrite 18i20 linked thru ADAT to a Behringer ADA8200 8 channel preamp to use an extra 3-4 inputs. Also using Audix mics on the toms. If I went with switching to Native Instruments I would have to at least get an interface with 4 preamps and still use ADAT to get all inputs I need.