How important is the matching of the DAC to the Amp. I see a few people who buy their amps and DAC from the same company. Is this due to company loyalty or do companies gear DACs in a way that provides more quality when used with their product?

Hey guys. Long time reader, first time poster. I have had my Sennheiser HD 600s for a few years now. Before that, I only had the budget for headphones that were less than $100. HD 600s broke my bank and for these years I haven't really had a budget for new audio equipment (can you tell I can't...