I don't know if anyone has ever tried upgrading the 5532's in this crossover but I decided I would upgrade to OPA627 on a BrownDog adaptor pcb to see what all the fuss was about. Well the improvement was outstanding, clearer bottom end, much much cleaner mids and a more lively top end yet an overall smoother sound but still dynamic as all hell on my 4435's, for those of you still using this xover I can highly recommend this mod. I purchased mine from this ebay store http://stores.ebay.com.au/Parts-and-Audio but you can also get them direct from BrownDog http://cimarrontechnology.com/index.asp no affilliation. I haven't replaced the TLO74's yet as I understand they are still quite reasonable performers even by todays standards. But I will now go through my amps and bits and pieces to replace whatever they have used on the front end with these little gems, truley worth the effort IMHO. I have used 5532's for years but did'nt realise how ordinary they are. .