If your going to go a DIY or get a passive job get a used NAD 218THX amp.225 wpc stereo and if you read the stereophile review the reviewer saidf it might be a bit thick in the mids but had more bass slam than any amp hje had revieed.You can pick it up used for less than $500 and if I remember corerctly it had like 700 wpc mono.Another budget candidate would be the 300 wpc stereo Adcom 5802.Gobs of power for less than $800 used.But in all myu experience nothing had the bass "traction" and controll of Krell.One of their class A/B amps from 150 or 225 on up converted to mono would givbe you a "grip,slam,and control" that others just can't deliver.For full range even their class A amps have a brittle/metallic mid range that some either like or overlook because of their virtues fo clear treble and bass control but for a passive amp or DDIY it would be the best.Freinds I have in pro audio might say Crown (bullet proof) like a DC300 but you can go with a lot of options with a bass amp you might not consioder for your mains.
Chazzbo
Chazzbo