There are lots of good choices, as the others have indicated. One thing that might help to better focus the recommendations would be to indicate the specific make and model of the speaker (which apparently is not the one indicated in your system description). A given 300b amp, especially a SET, can sound different depending on the impedance characteristics of the speakers it is being used with, particularly if the impedance varies significantly as a function of frequency and/or does not remain high at all frequencies.
For example the T-1500, unusually among SETs, uses 6 db of negative feedback to achieve a relatively low output impedance/high damping factor. That will reduce its sensitivity to the speaker's variations of impedance as a function of frequency, while also (I would expect) contributing to differences between its intrinsic sonic character and that of other SETs.
Good luck. Regards,
-- Al
