Thanks for the comprehensive response, and the additional background. In addition to the suggestions the others have offered, if I were in your shoes, those shoes including the possibility of eventually replacing your GoldenEar Triton 7 speakers with a pair of Maggies, what I would consider doing is purchasing something like this Ayre V-5xe power amp, which is presently being offered here at $2900, apparently having cost $5950 originally. I would initially drive it with the preamp section of your Sphinx, and at a later time, if and when you feel the urge and finances allow, address the possibility of a preamp upgrade.
The V-5xe is rated at 150W into 8 ohms, and would double that to 300W into the 4 ohm impedance of a Maggie.
From Stereophile’s "Recommended Components 2012," in which this amp was rated "Class A," along with several other solid state amps costing up to $106K:
The compact, beautifully built V-5xe delivers 150Wpc into 8 ohms and features single-ended and balanced inputs and speaker-wire terminals made by Cardas. Though it lacked some power in the bass and sacrificed “a little of that you-are-there-ness” produced by the best single-ended-triode amps, the V-5xe offered a highly resolving, dynamic, harmonically pleasing sound that was never fatiguing. “Open, airy, and sweet,” said ST. “What more do you want?” (Vol.29 No.5)My feeling is that pursuing a path such as that is likely to provide you with a more meaningful sonic upgrade at this time than investing a similar amount of money in at least most comparably powerful integrateds or preamp/power amp combos. While also being sufficiently powerful and of sufficient calibre sonically to be future-proof with respect to whatever speaker upgrade and/or preamp upgrade you may eventually choose to do.
I have no affiliation with or knowledge of the seller.
Good luck. Best regards,
-- Al