Tweakers' Asylum: TDA1541A sin(x)/x, I/V ... do I get this right by MBK

Hi all,

after reading more I have the impression I start getting a grip. Many black holes still there though. So am I getting this right:
1- after non-oversampling mod in my 1541 equipped Rotel I now have a 44.1 kHz stepped output with all aliases present
2- these aliases past 22 kHz cause attenuation of sin(x)/x form and of course HF down the road that may cause problems (though it sounds fine to me in raw form, right now the original NE5532 and original analog filter are still in there).
3- to fix phase error close to 20 kHz and to get rid of HF aliases, thus fixing the sin(x)/x as well, passive 3 pole Bessel filters have been proposed after resistor based I/V conversion and subsequent transformer gain stage and tube gain stage. Alternately, I/V and nothing after that.

Problem:

I'd like to avoid transformers and tubes but like to put a suitable sin(x)/x filter anyway. May be op amp based (reason: passive I/V w/o transformers and tubes need gain somewhere, the rest of my chain is SS and I use active x-o's in my speakers AND op-amp chip amplifiers to one lonely tube somewhere won't make it a tube system anyway).

Questions:

1- to avoid loading op-amps with HF, may one do a passive I/V immediately followed by a passive sin(x)/x filter before the first op amp gain stage? Does that make sense at all? I'd think it saves the first op amp some HF load
2- the cutoff point and construction/calculation of this 3 pole Bessel lowpass is somehow lost on me (20 kHz?), anywhere in archives or datasheets I can only find it mentioned as "trivial" hahahaha...
3- if no passive filter before further gain is possible (that means, op amp pick up) how about an 4th order L-R after op-amp buffer, instead (the buffer takes the full brunt of the aliases though); I built those for my speaker x-o's so at least I'm on safer terrain here...

Thanks,

MBK