Like nsgarch I feel your reciever is the choke point in your system.You did not mention the type of speakers you are driving or the number.Why not consider selling the Pioneer? adding the amount you would have payed for the AcousTech[my choice out of the phono stages you mentioned] and buy a high quality integrated with a phono stage built in.Then any mods you make to arm or cartridge will be audible improvements instead of being converted to over processed transistor hell.Or you could buy the AcousTech not expect too much and when you upgrade to a line stage integrated be blown away by the improvement.
Should I purchase an expensive phono preamp
I have a Nottingham Horizon TT with the Rega 250 arm and a Goldring 1000 series MM cartridge. This is hooked up to a Pioneer Elite VSX-99 AV receiver that has a built in phono stage. I am trying to improve on the phono stage but I am wondering if there will be diminishing returns going to the more expensive stages. I am considering Lehmann BC, Graham Slee Era Gold V and AcousTech PH-1. I listen to Jazz, Old School R&B and Classic Rock music mainly.